diff --git a/.github/workflows/draft-pdf.yml b/.github/workflows/draft-pdf.yml
index 76310246..a349ebaa 100644
--- a/.github/workflows/draft-pdf.yml
+++ b/.github/workflows/draft-pdf.yml
@@ -14,7 +14,7 @@ jobs:
           # This should be the path to the paper within your repo.
           paper-path: paper/paper.md
       - name: Upload
-        uses: actions/upload-artifact@v1
+        uses: actions/upload-artifact@v4
         with:
           name: paper
           # This is the output path where Pandoc will write the compiled
diff --git a/Project.toml b/Project.toml
index 3aab73fe..37cb96a1 100644
--- a/Project.toml
+++ b/Project.toml
@@ -5,6 +5,7 @@ version = "0.10.32"
 
 [deps]
 AbstractTrees = "1520ce14-60c1-5f80-bbc7-55ef81b5835c"
+Accessors = "7d9f7c33-5ae7-4f3b-8dc6-eff91059b697"
 ArraysOfArrays = "65a8f2f4-9b39-5baf-92e2-a9cc46fdf018"
 BitIntegers = "c3b6d118-76ef-56ca-8cc7-ebb389d030a1"
 CodecLz4 = "5ba52731-8f18-5e0d-9241-30f10d1ec561"
@@ -32,6 +33,7 @@ XXHashNative = "e5d8e439-e7fa-4681-9c12-1c64bda517be"
 
 [compat]
 AbstractTrees = "^0.4"
+Accessors = "0.1.36"
 Aqua = "^0.8"
 ArraysOfArrays = "^0.6"
 Arrow = "~2.7.1"
@@ -54,6 +56,7 @@ Parameters = "^0.12"
 Pkg = "^1.0"
 PrecompileTools = "^1.2.0"
 PrettyTables = "^2.1"
+Random = "^1.0"
 SHA = "^0.7, ^1.0"
 SentinelArrays = "^1.3"
 StaticArrays = "^1"
@@ -72,10 +75,11 @@ DataFrames = "a93c6f00-e57d-5684-b7b6-d8193f3e46c0"
 InteractiveUtils = "b77e0a4c-d291-57a0-90e8-8db25a27a240"
 LorentzVectors = "3f54b04b-17fc-5cd4-9758-90c048d965e3"
 Pkg = "44cfe95a-1eb2-52ea-b672-e2afdf69b78f"
+Random = "9a3f8284-a2c9-5f02-9a11-845980a1fd5c"
 SHA = "ea8e919c-243c-51af-8825-aaa63cd721ce"
 StaticArrays = "90137ffa-7385-5640-81b9-e52037218182"
 TOML = "fa267f1f-6049-4f14-aa54-33bafae1ed76"
 Test = "8dfed614-e22c-5e08-85e1-65c5234f0b40"
 
 [targets]
-test = ["Aqua", "Arrow", "DataFrames", "InteractiveUtils", "LorentzVectors", "Pkg", "SHA", "StaticArrays", "TOML", "Test"]
+test = ["Aqua", "Arrow", "DataFrames", "InteractiveUtils", "LorentzVectors", "Pkg", "Random", "SHA", "StaticArrays", "TOML", "Test"]
diff --git a/src/RNTuple/Writing/Stubs.jl b/src/RNTuple/Writing/Stubs.jl
new file mode 100644
index 00000000..8bd7df97
--- /dev/null
+++ b/src/RNTuple/Writing/Stubs.jl
@@ -0,0 +1,97 @@
+module Stubs
+using ..UnROOT
+
+const file_preamble = [
+    0x72, 0x6F, 0x6F, 0x74, 0x00, 0x00, 0xF7, 0x45,
+]
+
+const fileheader = UnROOT.FileHeader32(100, 0x00000643, 0x00000604, 63, 1, 84, 0x04, 0, 0x00000461, 419, UInt8[0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00])
+const dummy_padding1 = [
+    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+    0x00, 0x00, 0x00, 0x00, 0x00,
+]
+
+const tkey32_tfile = UnROOT.TKey32(144, 4, 86, 0x7567176d, 58, 1, 100, 0, "TFile", "test_ntuple_minimal.root", "")
+const tfile = UnROOT.TFile_write("test_ntuple_minimal.root", "")
+const tdirectory32 = UnROOT.ROOTDirectoryHeader32(5, 0x7567176d, 0x7567176d, 121, 84, 100, 0, 1000)
+const dummy_padding2 = [
+    0x00, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+]
+
+
+const RBlob1 = UnROOT.RBlob(0x00DC, 0x0004, 0x000000BA, 0x7567176D, 0x0022, 0x0001, 244, 100, "RBlob", "", "")
+const rnt_header = UnROOT.RNTupleHeader(zero(UInt64), "myntuple", "", "ROOT v6.33.01", [
+    UnROOT.FieldRecord(zero(UInt32), zero(UInt32), zero(UInt32), zero(UInt16), zero(UInt16), 0, "one_uint", "std::uint32_t", "", ""),
+], [UnROOT.ColumnRecord(0x14, 0x20, zero(UInt32), zero(UInt32), 0),], UnROOT.AliasRecord[], UnROOT.ExtraTypeInfo[])
+    
+
+const RBlob2 = UnROOT.RBlob(0x0026, 0x0004, 0x00000004, 0x7567176D, 0x0022, 0x0001, 0x01D0, 100, "RBlob", "", "")
+const page1 = [
+    0xCE, 0xCE, 0xCE, 0xCE,
+]
+
+const RBlob3 = UnROOT.RBlob(0x009E, 0x0004, 0x0000007C, 0x7567176D, 0x0022, 0x0001, 0x01F6, 100, "RBlob", "", "")
+const cluster_summary = UnROOT.Write_RNTupleListFrame([UnROOT.ClusterSummary(0, 1)])
+const nested_page_locations = 
+UnROOT.RNTuplePageTopList([
+    UnROOT.RNTuplePageOuterList([
+        UnROOT.RNTuplePageInnerList([
+            UnROOT.PageDescription(0x00000001, UnROOT.Locator(4, 0x00000000000001f2, )),
+        ]),
+    ]),
+])
+const pagelink = UnROOT.PageLink(0x3dec59c009c67e28, cluster_summary.payload, nested_page_locations)
+
+const RBlob4 = UnROOT.RBlob(0x00CE, 0x0004, 0x000000AC, 0x7567176D, 0x0022, 0x0001, 0x0294, 100, "RBlob", "", "")
+const rnt_footer = UnROOT.RNTupleFooter(0, 0x3dec59c009c67e28, UnROOT.RNTupleSchemaExtension([], [], [], []), [], [
+    UnROOT.ClusterGroupRecord(0, 1, 1, UnROOT.EnvLink(0x000000000000007c, UnROOT.Locator(124, 0x0000000000000218, ))),
+], UnROOT.EnvLink[])
+const tkey32_anchor = UnROOT.TKey32(134, 4, 70, 0x7567176d, 64, 1, 866, 100, "ROOT::Experimental::RNTuple", "myntuple", "")
+# these 6 bytes are between tkey32_anchor and the actual anchor
+const magic_6bytes = [0x40, 0x00, 0x00, 0x42, 0x00, 0x04]
+
+const rnt_anchor = UnROOT.ROOT_3a3a_Experimental_3a3a_RNTuple(0x0000, 0x0002, 0x0000, 0x0000, 0x0000000000000116, 0x00000000000000ba, 0x00000000000000ba, 0x00000000000002b6, 0x00000000000000ac, 0x00000000000000ac, 0xdc495fd01479af1b)
+const tkey32_TDirectory = UnROOT.TKey32(121, 4, 68, 0x7567176d, 53, 1, 1000, 100, "", "test_ntuple_minimal.root", "")
+# 1 key, and it is the RNTuple Anchor
+const n_keys = [
+    0x00, 0x00, 0x00, 0x01,
+]
+
+
+const tkey32_TStreamerInfo = UnROOT.TKey32(419, 4, 1266, 0x7567176d, 64, 1, 1121, 100, "TList", "StreamerInfo", "Doubly linked list")
+
+const tsreamerinfo_compressed = [
+    0x5A, 0x4C, 0x08, 0x5A, 0x01, 0x00, 0xF2, 0x04, 0x00, 0x78, 0x01, 0xBD, 0x92, 0x4D, 0x4E, 0xC2,
+    0x40, 0x1C, 0xC5, 0x1F, 0x05, 0x13, 0x91, 0x8F, 0xAD, 0x1A, 0x36, 0x6E, 0xBD, 0x42, 0x57, 0x15,
+    0x83, 0x91, 0x44, 0x29, 0x42, 0xC5, 0x68, 0x82, 0x66, 0x80, 0x29, 0x94, 0x8F, 0x99, 0x66, 0xDA,
+    0x26, 0xB2, 0x63, 0xE7, 0x69, 0xBC, 0x84, 0x97, 0xD0, 0x53, 0x78, 0x05, 0xFD, 0x77, 0x24, 0x04,
+    0x12, 0x89, 0x68, 0x83, 0x2F, 0x99, 0x69, 0x3B, 0xED, 0xBC, 0x5F, 0xFB, 0x5E, 0x2D, 0x64, 0xDE,
+    0xB1, 0x83, 0x14, 0x48, 0x46, 0x3C, 0x91, 0x52, 0x16, 0x32, 0x6F, 0x1F, 0x24, 0xA7, 0x19, 0x2A,
+    0xCE, 0x26, 0x5C, 0x55, 0x85, 0x2B, 0x41, 0xAB, 0x2F, 0xC8, 0x5A, 0xC0, 0x31, 0x3D, 0xAE, 0x37,
+    0xA4, 0x69, 0x2E, 0x35, 0x6C, 0xDB, 0x31, 0xCD, 0xCA, 0xA3, 0xCF, 0x95, 0x37, 0xE1, 0x22, 0x64,
+    0x63, 0xD3, 0x6C, 0xD4, 0x9C, 0xC8, 0x1F, 0x73, 0xB4, 0xF3, 0xCF, 0x55, 0x32, 0xCC, 0xD0, 0xD6,
+    0x27, 0x6D, 0x68, 0x77, 0x86, 0x27, 0x4A, 0xB1, 0x69, 0x6C, 0x16, 0x21, 0xBD, 0xCA, 0xCD, 0xC5,
+    0x70, 0xF2, 0x8F, 0x56, 0xD8, 0x65, 0x16, 0x78, 0x5D, 0x67, 0xEA, 0xF3, 0xF8, 0xD6, 0x1D, 0x0C,
+    0x9A, 0x9D, 0xD8, 0x11, 0xA5, 0xC5, 0x6B, 0x00, 0x28, 0xB8, 0x2D, 0xAE, 0x02, 0x4F, 0x8A, 0x8A,
+    0x2F, 0xBB, 0x03, 0x5A, 0x40, 0x9E, 0x86, 0x11, 0x9F, 0xAC, 0x53, 0x31, 0x12, 0x81, 0xD7, 0x17,
+    0xBC, 0x77, 0x14, 0x0C, 0xA4, 0x0A, 0x2D, 0xA0, 0x33, 0x03, 0x5E, 0xE9, 0xF8, 0x33, 0xE5, 0x92,
+    0x0D, 0xA5, 0x8A, 0x8D, 0xB7, 0x4B, 0xF1, 0xC4, 0x3F, 0x50, 0xEA, 0x2C, 0xFC, 0x73, 0x62, 0x0F,
+    0xF3, 0xC4, 0x6E, 0x60, 0x58, 0xC0, 0x95, 0xEE, 0xE5, 0x70, 0xB9, 0x97, 0x9C, 0xDB, 0xE4, 0x7C,
+    0x74, 0xCE, 0x59, 0x8F, 0xEB, 0xBC, 0x8A, 0x00, 0x76, 0x69, 0xAC, 0x55, 0x61, 0xD1, 0xCA, 0x58,
+    0x8A, 0xBE, 0x05, 0xB0, 0xD9, 0x57, 0x29, 0xB7, 0x30, 0xE8, 0xAA, 0xF9, 0x5D, 0xF5, 0xB5, 0xF2,
+    0x34, 0xE4, 0x41, 0x12, 0xC8, 0xFD, 0x1C, 0xD2, 0xD2, 0x90, 0xBA, 0x86, 0x1C, 0x2C, 0x7F, 0xC7,
+    0x9E, 0x7B, 0xC1, 0x45, 0x12, 0xC2, 0x86, 0x49, 0x9D, 0x49, 0x19, 0x6E, 0x3D, 0xA9, 0x24, 0x90,
+    0xCD, 0x92, 0x4A, 0x42, 0x68, 0xCF, 0xBB, 0xB8, 0xD6, 0x5D, 0xD8, 0xBA, 0x8B, 0xFD, 0xE5, 0x2E,
+    0xB2, 0xEE, 0xE9, 0x80, 0x77, 0x47, 0x41, 0x34, 0x01, 0xE9, 0x97, 0x7F, 0x14, 0x3E, 0x01, 0x15,
+    0x3D, 0xC1, 0xCA,
+]
+
+const tfile_end = [
+    0x00, 0x00, 0x00, 0x3F, 0x00, 0x04, 0x00, 0x00, 0x00, 0x0A, 0x75, 0x67, 0x17, 0x6D, 0x00, 0x35,
+    0x00, 0x01, 0x00, 0x00, 0x06, 0x04, 0x00, 0x00, 0x00, 0x64, 0x00, 0x18, 0x74, 0x65, 0x73, 0x74,
+    0x5F, 0x6E, 0x74, 0x75, 0x70, 0x6C, 0x65, 0x5F, 0x6D, 0x69, 0x6E, 0x69, 0x6D, 0x61, 0x6C, 0x2E,
+    0x72, 0x6F, 0x6F, 0x74, 0x00, 0x00, 0x01, 0x00, 0x00, 0x06, 0x43, 0x77, 0x35, 0x94, 0x00,
+]
+end
diff --git a/src/RNTuple/Writing/TFileWriter.jl b/src/RNTuple/Writing/TFileWriter.jl
new file mode 100644
index 00000000..ec40d797
--- /dev/null
+++ b/src/RNTuple/Writing/TFileWriter.jl
@@ -0,0 +1,565 @@
+using StaticArrays
+using UnROOT
+using UnROOT: RNTupleFrame, ClusterSummary, PageDescription
+using XXHashNative: xxh3_64
+using Accessors
+using Tables: istable, columntable, schema
+
+function color_diff(ary1, ary2)
+    if length(ary1) != length(ary2)
+        printstyled("!!! Length mismatch !!!: length(ary1)=$(length(ary1)), length(ary2)=$(length(ary2))\n", color=:red)
+    end
+    print("[")
+    x = 0
+    for (i,j) in zip(ary1, ary2)
+        if x % 8 == 0
+            print("    ")
+        end
+        if x % 16 == 0
+            println()
+            x = 0
+        end
+        if i != j
+            printstyled("$(repr(i))/$(repr(j)), ", color=:red)
+        else
+            printstyled("$(repr(i)), ", color=:green)
+        end
+        x += 1
+    end
+    println()
+    println("]")
+end
+
+function rnt_write(io::IO, x::AbstractString; legacy=false)
+    L = length(x)
+    if legacy
+        if L > typemax(UInt8)
+            error("String longer than 255 not implemented")
+        end
+        write(io, UInt8(L))
+        write(io, codeunits(x))
+    else
+        write(io, UInt32(L))
+        write(io, codeunits(x))
+    end
+end
+
+function rnt_write(io::IO, x::AbstractVector)
+    error("Ambiguous type: $(typeof(x)), use Write_RNTupleListFrame or similar wrapper")
+end
+
+function rnt_write(io::IO, x; legacy=false)
+    if legacy
+        write(io, bswap(x))
+    else
+        write(io, x)
+    end
+end
+
+function rnt_write(io::IO, x::AbstractVector{UInt8}; legacy=false)
+    if legacy
+        write(io, reverse(x))
+    else
+        write(io, x)
+    end
+end
+
+function test_io(obj, expected; kw...)
+    a = IOBuffer()
+    rnt_write(a, obj; kw...)
+    ours = take!(a)
+    if ours != expected
+        color_diff(ours, expected)
+    end
+end
+
+function rnt_write(io::IO, x::UnROOT.FileHeader32)
+    rnt_write(io, x.fBEGIN; legacy=true)
+    rnt_write(io, x.fEND; legacy=true)
+    rnt_write(io, x.fSeekFree; legacy=true)
+    rnt_write(io, x.fNbytesFree; legacy=true)
+    rnt_write(io, x.nfree; legacy=true)
+    rnt_write(io, x.fNbytesName; legacy=true)
+    rnt_write(io, x.fUnits; legacy=true)
+    rnt_write(io, x.fCompress; legacy=true)
+    rnt_write(io, x.fSeekInfo; legacy=true)
+    rnt_write(io, x.fNbytesInfo; legacy=true)
+    rnt_write(io, x.fUUID; legacy=true)
+end
+
+function rnt_write(io::IO, x::UnROOT.TKey32)
+    p = position(io)
+    rnt_write(io, x.fNbytes; legacy=true)
+    rnt_write(io, x.fVersion; legacy=true)
+    rnt_write(io, x.fObjlen; legacy=true)
+    rnt_write(io, x.fDatime; legacy=true)
+    rnt_write(io, x.fKeylen; legacy=true)
+    rnt_write(io, x.fCycle; legacy=true)
+    rnt_write(io, x.fSeekKey; legacy=true)
+    rnt_write(io, x.fSeekPdir; legacy=true)
+    rnt_write(io, x.fClassName; legacy=true)
+    rnt_write(io, x.fName; legacy=true)
+    rnt_write(io, x.fTitle; legacy=true)
+    @assert position(io) - p == x.fKeylen
+end
+
+struct TFile_write
+    filename::String
+    unknown::String
+end
+function rnt_write(io::IO, x::TFile_write)
+    rnt_write(io, x.filename; legacy=true)
+    rnt_write(io, x.unknown; legacy=true)
+end
+
+function rnt_write(io::IO, x::UnROOT.ROOTDirectoryHeader32)
+    rnt_write(io, x.fVersion; legacy=true)
+    rnt_write(io, x.fDatimeC; legacy=true)
+    rnt_write(io, x.fDatimeM; legacy=true)
+    rnt_write(io, x.fNbytesKeys; legacy=true)
+    rnt_write(io, x.fNbytesName; legacy=true)
+    rnt_write(io, x.fSeekDir; legacy=true)
+    rnt_write(io, x.fSeekParent; legacy=true)
+    rnt_write(io, x.fSeekKeys; legacy=true)
+end
+
+struct RBlob
+    fNbytes::Int32
+    fVersion::Int16
+    fObjLen::Int32
+    fDatime::UInt32
+    fKeyLen::Int16
+    fCycle::Int16
+    fSeekKey::Int32
+    fSeekPdir::Int32
+    fClassName::String
+    fName::String
+    fTitle::String
+end
+function rnt_write(io::IO, x::RBlob)
+    rnt_write(io, x.fNbytes; legacy=true)
+    rnt_write(io, x.fVersion; legacy=true)
+    rnt_write(io, x.fObjLen; legacy=true)
+    rnt_write(io, x.fDatime; legacy=true)
+    rnt_write(io, x.fKeyLen; legacy=true)
+    rnt_write(io, x.fCycle; legacy=true)
+    rnt_write(io, x.fSeekKey; legacy=true)
+    rnt_write(io, x.fSeekPdir; legacy=true)
+    rnt_write(io, x.fClassName; legacy=true)
+    rnt_write(io, x.fName; legacy=true)
+    rnt_write(io, x.fTitle; legacy=true)
+end
+
+function rnt_write(io::IO, x::UnROOT.FieldRecord)
+    rnt_write(io, x.field_version)
+    rnt_write(io, x.type_version)
+    rnt_write(io, x.parent_field_id)
+    rnt_write(io, x.struct_role)
+    rnt_write(io, x.flags)
+    if !iszero(x.repetition)
+        if x.flags != 0x01
+            error("Repetition is set but flags is not 0x01")
+        end
+        rnt_write(io, x.repetition)
+    end
+    rnt_write(io, x.field_name)
+    rnt_write(io, x.type_name)
+    rnt_write(io, x.type_alias)
+    rnt_write(io, x.field_desc)
+end
+
+function rnt_write(io::IO, x::UnROOT.ColumnRecord)
+    rnt_write(io, x.type)
+    rnt_write(io, x.nbits)
+    rnt_write(io, x.field_id)
+    rnt_write(io, x.flags)
+    if !iszero(x.first_ele_idx)
+        if x.flags != 0x08
+            error("First element index is set but flags is not 0x08")
+        end
+        rnt_write(io, x.first_ele_idx)
+    end
+end
+
+function rnt_write(io::IO, x::RNTupleFrame{T}) where T
+    temp_io = IOBuffer()
+    rnt_write(temp_io, x.payload)
+    size = temp_io.size + 8
+    write(io, Int64(size))
+    seekstart(temp_io)
+    write(io, temp_io)
+end
+
+struct Write_RNTupleListFrame{T<:AbstractArray}
+    payload::T
+end
+function rnt_write(io::IO, x::Write_RNTupleListFrame)
+    ary = x.payload
+    N = length(ary)
+    temp_io = IOBuffer()
+    for x in ary
+        rnt_write(temp_io, RNTupleFrame(x))
+    end
+    size = temp_io.size + sizeof(Int64) + sizeof(Int32)
+    write(io, Int64(-size))
+    write(io, Int32(N))
+    seekstart(temp_io)
+    write(io, temp_io)
+end
+
+function _checksum(x::UnROOT.RNTupleHeader)
+    temp_io = IOBuffer()
+    rnt_write(temp_io, x.feature_flag)
+    rnt_write(temp_io, x.name)
+    rnt_write(temp_io, x.ntuple_description)
+    rnt_write(temp_io, x.writer_identifier)
+    rnt_write(temp_io, Write_RNTupleListFrame(x.field_records))
+    rnt_write(temp_io, Write_RNTupleListFrame(x.column_records))
+    rnt_write(temp_io, Write_RNTupleListFrame(x.alias_columns))
+    rnt_write(temp_io, Write_RNTupleListFrame(x.extra_type_infos))
+
+    # add id_length size and checksum size
+    envelope_size = temp_io.size + sizeof(Int64) + sizeof(UInt64)
+    id_type = 0x0001
+
+    id_length = (UInt64(envelope_size & 0xff) << 16) | id_type
+
+    payload_ary = take!(temp_io)
+    prepend!(payload_ary, reinterpret(UInt8, [id_length]))
+
+    return xxh3_64(payload_ary)
+end
+
+function rnt_write(io::IO, x::UnROOT.RNTupleHeader; envelope=true)
+    temp_io = IOBuffer()
+    rnt_write(temp_io, x.feature_flag)
+    rnt_write(temp_io, x.name)
+    rnt_write(temp_io, x.ntuple_description)
+    rnt_write(temp_io, x.writer_identifier)
+    rnt_write(temp_io, Write_RNTupleListFrame(x.field_records))
+    rnt_write(temp_io, Write_RNTupleListFrame(x.column_records))
+    rnt_write(temp_io, Write_RNTupleListFrame(x.alias_columns))
+    rnt_write(temp_io, Write_RNTupleListFrame(x.extra_type_infos))
+
+    # add id_length size and checksum size
+    envelope_size = temp_io.size + sizeof(Int64) + sizeof(UInt64)
+    id_type = 0x0001
+
+    id_length = (UInt64(envelope_size & 0xff) << 16) | id_type
+
+    payload_ary = take!(temp_io)
+
+    if envelope
+        prepend!(payload_ary, reinterpret(UInt8, [id_length]))
+        checksum = xxh3_64(payload_ary)
+        write(io, payload_ary)
+        write(io, checksum)
+    else
+        write(io, payload_ary)
+    end
+end
+
+function rnt_write(io::IO, x::ClusterSummary)
+    rnt_write(io, x.first_entry_number)
+    rnt_write(io, x.number_of_entries)
+end
+
+function rnt_write(io::IO, x::UnROOT.Locator)
+    rnt_write(io, x.num_bytes)
+    rnt_write(io, x.offset)
+end
+
+function rnt_write(io::IO, x::PageDescription)
+    rnt_write(io, x.num_elements)
+    rnt_write(io, x.locator)
+end
+
+function rnt_write(io::IO, x::UnROOT.RNTuplePageTopList)
+    ary = x.payload
+    N = length(ary)
+    temp_io = IOBuffer()
+    for x in ary
+        rnt_write(temp_io, x)
+    end
+    size = temp_io.size + sizeof(Int64) + sizeof(Int32)
+    write(io, Int64(-size))
+    write(io, Int32(N))
+    seekstart(temp_io)
+    write(io, temp_io)
+end
+function rnt_write(io::IO, x::UnROOT.RNTuplePageOuterList)
+    ary = x.payload
+    N = length(ary)
+    temp_io = IOBuffer()
+    for x in ary
+        rnt_write(temp_io, x)
+    end
+    size = temp_io.size + sizeof(Int64) + sizeof(Int32)
+    write(io, Int64(-size))
+    write(io, Int32(N))
+    seekstart(temp_io)
+    write(io, temp_io)
+end
+function rnt_write(io::IO, x::UnROOT.RNTuplePageInnerList)
+    ary = x.payload
+    N = length(ary)
+    temp_io = IOBuffer()
+    for x in ary
+        rnt_write(temp_io, x)
+    end
+    offset = zero(UInt64)
+    compression = zero(UInt32)
+    write(temp_io, offset, compression)
+    size = temp_io.size + sizeof(Int64) + sizeof(Int32)
+    write(io, Int64(-size))
+    write(io, Int32(N))
+    seekstart(temp_io)
+    write(io, temp_io)
+end
+
+function rnt_write(io::IO, x::UnROOT.PageLink; envelope=true)
+    temp_io = IOBuffer()
+    rnt_write(temp_io, x.header_checksum)
+    rnt_write(temp_io, Write_RNTupleListFrame(x.cluster_summaries))
+    rnt_write(temp_io, x.nested_page_locations)
+
+    # add id_length size and checksum size
+    envelope_size = temp_io.size + sizeof(Int64) + sizeof(UInt64)
+    id_type = 0x0003
+
+    id_length = (UInt64(envelope_size & 0xff) << 16) | id_type
+
+    payload_ary = take!(temp_io)
+
+    if envelope
+        prepend!(payload_ary, reinterpret(UInt8, [id_length]))
+        checksum = xxh3_64(payload_ary)
+        write(io, payload_ary)
+        write(io, checksum)
+    else
+        write(io, payload_ary)
+    end
+end
+
+function rnt_write(io::IO, x::UnROOT.EnvLink)
+    rnt_write(io, x.uncomp_size)
+    rnt_write(io, x.locator)
+end
+
+"""
+@SimpleStruct struct ClusterGroupRecord
+    minimum_entry_number::Int64
+    entry_span::Int64
+    num_clusters::Int32
+    page_list_link::EnvLink
+end
+"""
+function rnt_write(io::IO, x::UnROOT.ClusterGroupRecord)
+    rnt_write(io, x.minimum_entry_number)
+    rnt_write(io, x.entry_span)
+    rnt_write(io, x.num_clusters)
+    rnt_write(io, x.page_list_link)
+end
+
+function rnt_write(io::IO, x::UnROOT.RNTupleSchemaExtension)
+    temp_io = IOBuffer()
+    rnt_write(temp_io, Write_RNTupleListFrame(x.field_records))
+    rnt_write(temp_io, Write_RNTupleListFrame(x.column_records))
+    rnt_write(temp_io, Write_RNTupleListFrame(x.alias_records))
+    rnt_write(temp_io, Write_RNTupleListFrame(x.extra_type_info))
+
+    size = temp_io.size + sizeof(Int64)
+    write(io, Int64(size))
+    seekstart(temp_io)
+    write(io, temp_io)
+end
+
+function rnt_write(io::IO, x::UnROOT.RNTupleFooter; envelope=true)
+    temp_io = IOBuffer()
+    rnt_write(temp_io, x.feature_flag)
+    rnt_write(temp_io, x.header_checksum)
+    rnt_write(temp_io, x.extension_header_links)
+    rnt_write(temp_io, Write_RNTupleListFrame(x.column_group_records))
+    rnt_write(temp_io, Write_RNTupleListFrame(x.cluster_group_records))
+    rnt_write(temp_io, Write_RNTupleListFrame(x.meta_data_links))
+
+    # add id_length size and checksum size
+    envelope_size = temp_io.size + sizeof(Int64) + sizeof(UInt64)
+    id_type = 0x0002
+
+    id_length = (UInt64(envelope_size & 0xff) << 16) | id_type
+
+    payload_ary = take!(temp_io)
+
+    if envelope
+        prepend!(payload_ary, reinterpret(UInt8, [id_length]))
+        checksum = xxh3_64(payload_ary)
+        write(io, payload_ary)
+        write(io, checksum)
+    else
+        write(io, payload_ary)
+    end
+end
+
+function rnt_write(io::IO, x::UnROOT.ROOT_3a3a_Experimental_3a3a_RNTuple)
+    temp_io = IOBuffer()
+    rnt_write(temp_io, x.fVersionEpoch; legacy=true)
+    rnt_write(temp_io, x.fVersionMajor; legacy=true)
+    rnt_write(temp_io, x.fVersionMinor; legacy=true)
+    rnt_write(temp_io, x.fVersionPatch; legacy=true)
+    rnt_write(temp_io, x.fSeekHeader; legacy=true)
+    rnt_write(temp_io, x.fNBytesHeader; legacy=true)
+    rnt_write(temp_io, x.fLenHeader; legacy=true)
+    rnt_write(temp_io, x.fSeekFooter; legacy=true)
+    rnt_write(temp_io, x.fNBytesFooter; legacy=true)
+    rnt_write(temp_io, x.fLenFooter; legacy=true)
+    payload_ary = take!(temp_io)
+    checksum = xxh3_64(payload_ary)
+    rnt_write(io, payload_ary)
+    rnt_write(io, checksum; legacy=true)
+end
+
+mutable struct WriteObservable{O, T}
+    io::O
+    position::Int64
+    len::Int64
+    object::T
+end
+
+function Base.setindex!(io::WriteObservable, val, key::Symbol)
+    new_obj = set(io.object, PropertyLens(key), val)
+    io.object = new_obj
+    return io
+end
+
+function Base.setindex!(io::WriteObservable, dict::Dict)
+    for (key, val) in dict
+        new_obj = set(io.object, PropertyLens(key), val)
+        io.object = new_obj
+    end
+    return io
+end
+
+function flush!(o::WriteObservable) 
+    io = o.io
+    old_pos = position(io)
+
+    seek(io, o.position)
+    rnt_write(io, o.object)
+    seek(io, old_pos)
+
+    nothing
+end
+
+function rnt_write_observe(io::IO, x::T) where T
+    pos = position(io)
+    rnt_write(io, x)
+    len = position(io) - pos
+    WriteObservable(io, pos, len, x)
+end
+
+function split4_encode(src::AbstractVector{UInt8})
+    @views [src[1:4:end-3]; src[2:4:end-2]; src[3:4:end-1]; src[4:4:end]]
+end
+
+function write_rntuple(file::IO, table; file_name="test_ntuple_minimal.root", rntuple_name="myntuple")
+    if !istable(table)
+        error("RNTuple writing accepts object compatible with Tables.jl interface, got type $(typeof(table))")
+    end
+
+    input_schema = schema(table)
+    input_Ncols = length(input_schema.names)
+    if input_Ncols != 1
+        error("Currently, RNTuple writing only supports a single, UInt32 column, got $input_Ncols columns")
+    end
+    input_T = only(input_schema.types)
+    if input_T != UInt32
+        error("Currently, RNTuple writing only supports a single, UInt32 column, got type $input_T")
+    end
+    input_col = only(columntable(table))
+    input_length = length(input_col)
+    if input_length > 65535
+        error("Input too long: RNTuple writing currently only supports a single page (65535 elements)")
+    end
+
+
+    rntAnchor_update = Dict{Symbol, Any}()
+
+    file_preamble_obs = rnt_write_observe(file, Stubs.file_preamble)
+    fileheader_obs = rnt_write_observe(file, Stubs.fileheader)
+    dummy_padding1_obs = rnt_write_observe(file, Stubs.dummy_padding1)
+
+    fileheader_obs[:fBEGIN] = UInt32(position(file))
+
+    tkey32_tfile_obs = rnt_write_observe(file, Stubs.tkey32_tfile)
+    tkey32_tfile_obs[:fName] = file_name
+    tfile_obs = rnt_write_observe(file, Stubs.tfile)
+
+    tdirectory32_obs = rnt_write_observe(file, Stubs.tdirectory32)
+    dummy_padding2_obs = rnt_write_observe(file, Stubs.dummy_padding2)
+
+    RBlob1_obs = rnt_write_observe(file, Stubs.RBlob1)
+    rntAnchor_update[:fSeekHeader] = UInt32(position(file))
+    rnt_header = UnROOT.RNTupleHeader(zero(UInt64), rntuple_name, "", "ROOT v6.33.01", [
+    UnROOT.FieldRecord(zero(UInt32), zero(UInt32), zero(UInt32), zero(UInt16), zero(UInt16), 0,     string(only(input_schema.names)), "std::uint32_t", "", ""),
+    ], [UnROOT.ColumnRecord(0x14, 0x20, zero(UInt32), zero(UInt32), 0),], UnROOT.AliasRecord[], UnROOT.ExtraTypeInfo[])
+
+    rnt_header_obs = rnt_write_observe(file, rnt_header)
+    rntAnchor_update[:fNBytesHeader] = rnt_header_obs.len
+    rntAnchor_update[:fLenHeader] = rnt_header_obs.len
+
+    RBlob2_obs = rnt_write_observe(file, Stubs.RBlob2)
+    page1 = reinterpret(UInt8, input_col)
+    page1_bytes = split4_encode(page1)
+    page1_position = position(file)
+    page1_obs = rnt_write_observe(file, page1_bytes)
+
+    RBlob3_obs = rnt_write_observe(file, Stubs.RBlob3)
+    cluster_summary = Write_RNTupleListFrame([ClusterSummary(0, input_length)])
+    nested_page_locations = 
+    UnROOT.RNTuplePageTopList([
+        UnROOT.RNTuplePageOuterList([
+            UnROOT.RNTuplePageInnerList([
+                PageDescription(input_length, UnROOT.Locator(sizeof(input_T) * input_length, page1_position, )),
+            ]),
+        ]),
+    ])
+
+    # stub checksum 0x3dec59c009c67e28
+    pagelink = UnROOT.PageLink(_checksum(rnt_header_obs.object), cluster_summary.payload, nested_page_locations)
+    pagelink_position = position(file)
+    pagelink_obs = rnt_write_observe(file, pagelink)
+
+    RBlob4_obs = rnt_write_observe(file, Stubs.RBlob4)
+    rntAnchor_update[:fSeekFooter] = UInt32(position(file))
+    rnt_footer = UnROOT.RNTupleFooter(0, _checksum(rnt_header_obs.object), UnROOT.RNTupleSchemaExtension([], [], [], []), [], [
+        UnROOT.ClusterGroupRecord(0, input_length, 1, UnROOT.EnvLink(0x000000000000007c, UnROOT.Locator(124, pagelink_position, ))),
+    ], UnROOT.EnvLink[])
+    rnt_footer_obs = rnt_write_observe(file, rnt_footer)
+    rntAnchor_update[:fNBytesFooter] = 0xac
+    rntAnchor_update[:fLenFooter] = 0xac
+
+    tkey32_anchor_position = position(file)
+    tkey32_anchor = UnROOT.TKey32(134, 4, 70, 0x7567176d, 64, 1, tkey32_anchor_position, 100, "ROOT::Experimental::RNTuple", rntuple_name, "")
+    tkey32_anchor_obs1 = rnt_write_observe(file, tkey32_anchor)
+    magic_6bytes_obs = rnt_write_observe(file, Stubs.magic_6bytes)
+    rnt_anchor_obs = rnt_write_observe(file, Stubs.rnt_anchor)
+    Base.setindex!(rnt_anchor_obs, rntAnchor_update)
+
+    tdirectory32_obs[:fSeekKeys] = UInt32(position(file))
+    tkey32_TDirectory_obs = rnt_write_observe(file, Stubs.tkey32_TDirectory)
+    n_keys_obs = rnt_write_observe(file, Stubs.n_keys)
+    tkey32_anchor_obs2 = rnt_write_observe(file, tkey32_anchor)
+
+    fileheader_obs[:fSeekInfo] = UInt32(position(file))
+    tkey32_TStreamerInfo_obs = rnt_write_observe(file, Stubs.tkey32_TStreamerInfo)
+    tsreamerinfo_compressed_obs = rnt_write_observe(file, Stubs.tsreamerinfo_compressed)
+    fileheader_obs[:fSeekFree] = UInt32(position(file))
+    tfile_end_obs = rnt_write_observe(file, Stubs.tfile_end)
+    fileheader_obs[:fEND] = UInt32(position(file))
+
+    flush!(tkey32_tfile_obs)
+    flush!(tdirectory32_obs)
+    flush!(fileheader_obs)
+    flush!(rnt_anchor_obs)
+end
diff --git a/src/RNTuple/bootstrap.jl b/src/RNTuple/bootstrap.jl
index b2130e88..9ea9f61c 100644
--- a/src/RNTuple/bootstrap.jl
+++ b/src/RNTuple/bootstrap.jl
@@ -16,6 +16,9 @@ end
 function ROOT_3a3a_Experimental_3a3a_RNTuple(io, tkey::TKey, refs)
     local_io = datastream(io, tkey)
     skip(local_io, 6)
+    _before_anchor = position(local_io)
+    anchor_checksum = xxh3_64(read(local_io, 2*4 + 6*8))
+    seek(local_io, _before_anchor)
     anchor = ROOT_3a3a_Experimental_3a3a_RNTuple(;
                     fVersionEpoch = readtype(local_io, UInt16),
                     fVersionMajor = readtype(local_io, UInt16),
@@ -30,6 +33,9 @@ function ROOT_3a3a_Experimental_3a3a_RNTuple(io, tkey::TKey, refs)
                     fChecksum = readtype(local_io, UInt64),
                                        )
 
+    @assert anchor.fChecksum == anchor_checksum "RNtuple anchor checksum doesn't match"
+
+
     header_bytes = decompress_bytes(read_seek_nb(io, anchor.fSeekHeader, anchor.fNBytesHeader), anchor.fLenHeader)
     header_io = IOBuffer(header_bytes)
     header = _rntuple_read(header_io, RNTupleEnvelope{RNTupleHeader})
diff --git a/src/RNTuple/footer.jl b/src/RNTuple/footer.jl
index e0a9a006..8c825bec 100644
--- a/src/RNTuple/footer.jl
+++ b/src/RNTuple/footer.jl
@@ -101,26 +101,32 @@ end
     number_of_entries::Int64
 end
 
-struct RNTupleListNoFrame{T} <: AbstractVector{T}
-    payload::Vector{T}
-end
-Base.size(r::RNTupleListNoFrame) = size(r.payload)
-Base.getindex(r::RNTupleListNoFrame, i) = r.payload[i]
-Base.setindex!(r::RNTupleListNoFrame, v, i) = (r.payload[i] = v)
-# without the inner Frame for each item
-function _rntuple_read(io, ::Type{RNTupleListNoFrame{T}}) where T
-    pos = position(io)
-    Size = read(io, Int64)
-    @assert Size < 0
-    NumItems = read(io, Int32)
-    end_pos = pos - Size
-    res = T[_rntuple_read(io, T) for _=1:NumItems]
-    seek(io, end_pos)
-    return RNTupleListNoFrame(res)
+for x in (:RNTuplePageTopList, :RNTuplePageOuterList, :RNTuplePageInnerList)
+    @eval begin
+        struct ($x){T} <: AbstractVector{T}
+            payload::Vector{T}
+        end
+
+        function _rntuple_read(io, ::Type{$x{T}}) where T
+            pos = position(io)
+            Size = read(io, Int64)
+            @assert Size < 0
+            NumItems = read(io, Int32)
+            end_pos = pos - Size
+            res = T[_rntuple_read(io, T) for _=1:NumItems]
+            seek(io, end_pos)
+            return $x(res)
+        end
+
+        Base.size(r::$x) = size(r.payload)
+        Base.getindex(r::$x, i) = r.payload[i]
+        Base.setindex!(r::$x, v, i) = (r.payload[i] = v)
+        
+    end
 end
 
 @SimpleStruct struct PageLink
     header_checksum::UInt64
     cluster_summaries::Vector{ClusterSummary}
-    nested_page_locations::RNTupleListNoFrame{RNTupleListNoFrame{RNTupleListNoFrame{PageDescription}}}
+    nested_page_locations::RNTuplePageTopList{RNTuplePageOuterList{RNTuplePageInnerList{PageDescription}}}
 end
diff --git a/src/UnROOT.jl b/src/UnROOT.jl
index 6126c9cf..cddbb185 100644
--- a/src/UnROOT.jl
+++ b/src/UnROOT.jl
@@ -65,6 +65,9 @@ include("RNTuple/highlevel.jl")
 include("RNTuple/fieldcolumn_reading.jl")
 include("RNTuple/displays.jl")
 
+include("RNTuple/Writing/TFileWriter.jl")
+include("RNTuple/Writing/Stubs.jl")
+
 _maxthreadid() = @static if VERSION < v"1.9"
     Threads.nthreads()
 else
diff --git a/src/types.jl b/src/types.jl
index e3cb39f1..fc5e08b9 100644
--- a/src/types.jl
+++ b/src/types.jl
@@ -110,7 +110,7 @@ end
 
 iscompressed(t::T) where T<:Union{TKey, TBasketKey} = t.fObjlen != t.fNbytes - t.fKeylen
 origin(t::T) where T<:Union{TKey, TBasketKey} = iscompressed(t) ? -t.fKeylen : t.fSeekKey
-seekstart(io, t::T) where T<:Union{TKey, TBasketKey} = seek(io, t.fSeekKey + t.fKeylen)
+Base.seekstart(io, t::T) where T<:Union{TKey, TBasketKey} = seek(io, t.fSeekKey + t.fKeylen)
 
 datastream(io, tkey::TKey) = IOBuffer(decompress_datastreambytes(compressed_datastream(io, tkey), tkey))
 
diff --git a/test/RNTupleWriting/lowlevel.jl b/test/RNTupleWriting/lowlevel.jl
new file mode 100644
index 00000000..d01f3f03
--- /dev/null
+++ b/test/RNTupleWriting/lowlevel.jl
@@ -0,0 +1,365 @@
+using UnROOT: rnt_write, RNTupleFrame, ClusterSummary, PageDescription, Write_RNTupleListFrame, RBlob
+using XXHashNative: xxh3_64
+using Tables: columntable
+using Random
+
+const REFERENCE_BYTES = [
+    0x72, 0x6F, 0x6F, 0x74, 0x00, 0x00, 0xF7, 0x45, 0x00, 0x00, 0x00, 0x64, 0x00, 0x00, 0x06, 0x43,
+    0x00, 0x00, 0x06, 0x04, 0x00, 0x00, 0x00, 0x3F, 0x00, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00, 0x54,
+    0x04, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x04, 0x61, 0x00, 0x00, 0x01, 0xA3, 0x00, 0x00, 0x00,
+    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x90, 0x00, 0x04, 0x00, 0x00, 0x00, 0x56, 0x75, 0x67,
+    0x17, 0x6D, 0x00, 0x3A, 0x00, 0x01, 0x00, 0x00, 0x00, 0x64, 0x00, 0x00, 0x00, 0x00, 0x05, 0x54,
+    0x46, 0x69, 0x6C, 0x65, 0x18, 0x74, 0x65, 0x73, 0x74, 0x5F, 0x6E, 0x74, 0x75, 0x70, 0x6C, 0x65,
+    0x5F, 0x6D, 0x69, 0x6E, 0x69, 0x6D, 0x61, 0x6C, 0x2E, 0x72, 0x6F, 0x6F, 0x74, 0x00, 0x18, 0x74,
+    0x65, 0x73, 0x74, 0x5F, 0x6E, 0x74, 0x75, 0x70, 0x6C, 0x65, 0x5F, 0x6D, 0x69, 0x6E, 0x69, 0x6D,
+    0x61, 0x6C, 0x2E, 0x72, 0x6F, 0x6F, 0x74, 0x00, 0x00, 0x05, 0x75, 0x67, 0x17, 0x6D, 0x75, 0x67,
+    0x17, 0x6D, 0x00, 0x00, 0x00, 0x79, 0x00, 0x00, 0x00, 0x54, 0x00, 0x00, 0x00, 0x64, 0x00, 0x00,
+    0x00, 0x00, 0x00, 0x00, 0x03, 0xE8, 0x00, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0xDC, 0x00, 0x04, 0x00, 0x00, 0x00, 0xBA, 0x75, 0x67,
+    0x17, 0x6D, 0x00, 0x22, 0x00, 0x01, 0x00, 0x00, 0x00, 0xF4, 0x00, 0x00, 0x00, 0x64, 0x05, 0x52,
+    0x42, 0x6C, 0x6F, 0x62, 0x00, 0x00, 0x01, 0x00, 0xBA, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x08, 0x00, 0x00, 0x00, 0x6D, 0x79, 0x6E, 0x74, 0x75, 0x70,
+    0x6C, 0x65, 0x00, 0x00, 0x00, 0x00, 0x0D, 0x00, 0x00, 0x00, 0x52, 0x4F, 0x4F, 0x54, 0x20, 0x76,
+    0x36, 0x2E, 0x33, 0x33, 0x2E, 0x30, 0x31, 0xB7, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0x01,
+    0x00, 0x00, 0x00, 0x3D, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x08, 0x00, 0x00, 0x00, 0x6F,
+    0x6E, 0x65, 0x5F, 0x75, 0x69, 0x6E, 0x74, 0x0D, 0x00, 0x00, 0x00, 0x73, 0x74, 0x64, 0x3A, 0x3A,
+    0x75, 0x69, 0x6E, 0x74, 0x33, 0x32, 0x5F, 0x74, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+    0xE0, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0x01, 0x00, 0x00, 0x00, 0x14, 0x00, 0x00, 0x00,
+    0x00, 0x00, 0x00, 0x00, 0x14, 0x00, 0x20, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+    0xF4, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0x00, 0x00, 0x00, 0x00, 0xF4, 0xFF, 0xFF, 0xFF,
+    0xFF, 0xFF, 0xFF, 0xFF, 0x00, 0x00, 0x00, 0x00, 0x28, 0x7E, 0xC6, 0x09, 0xC0, 0x59, 0xEC, 0x3D,
+    0x00, 0x00, 0x00, 0x26, 0x00, 0x04, 0x00, 0x00, 0x00, 0x04, 0x75, 0x67, 0x17, 0x6D, 0x00, 0x22,
+    0x00, 0x01, 0x00, 0x00, 0x01, 0xD0, 0x00, 0x00, 0x00, 0x64, 0x05, 0x52, 0x42, 0x6C, 0x6F, 0x62,
+    0x00, 0x00, 0xCE, 0xCE, 0xCE, 0xCE, 0x00, 0x00, 0x00, 0x9E, 0x00, 0x04, 0x00, 0x00, 0x00, 0x7C,
+    0x75, 0x67, 0x17, 0x6D, 0x00, 0x22, 0x00, 0x01, 0x00, 0x00, 0x01, 0xF6, 0x00, 0x00, 0x00, 0x64,
+    0x05, 0x52, 0x42, 0x6C, 0x6F, 0x62, 0x00, 0x00, 0x03, 0x00, 0x7C, 0x00, 0x00, 0x00, 0x00, 0x00,
+    0x28, 0x7E, 0xC6, 0x09, 0xC0, 0x59, 0xEC, 0x3D, 0xDC, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
+    0x01, 0x00, 0x00, 0x00, 0x18, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+    0x00, 0x00, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0xC0, 0xFF, 0xFF, 0xFF,
+    0xFF, 0xFF, 0xFF, 0xFF, 0x01, 0x00, 0x00, 0x00, 0xCC, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
+    0x01, 0x00, 0x00, 0x00, 0xD8, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0x01, 0x00, 0x00, 0x00,
+    0x01, 0x00, 0x00, 0x00, 0x04, 0x00, 0x00, 0x00, 0xF2, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x1C, 0xA0, 0xDF, 0x2E,
+    0x25, 0x1E, 0x55, 0x4C, 0x00, 0x00, 0x00, 0xCE, 0x00, 0x04, 0x00, 0x00, 0x00, 0xAC, 0x75, 0x67,
+    0x17, 0x6D, 0x00, 0x22, 0x00, 0x01, 0x00, 0x00, 0x02, 0x94, 0x00, 0x00, 0x00, 0x64, 0x05, 0x52,
+    0x42, 0x6C, 0x6F, 0x62, 0x00, 0x00, 0x02, 0x00, 0xAC, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x28, 0x7E, 0xC6, 0x09, 0xC0, 0x59, 0xEC, 0x3D, 0x38, 0x00,
+    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0xF4, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0x00, 0x00,
+    0x00, 0x00, 0xF4, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0x00, 0x00, 0x00, 0x00, 0xF4, 0xFF,
+    0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0x00, 0x00, 0x00, 0x00, 0xF4, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
+    0xFF, 0xFF, 0x00, 0x00, 0x00, 0x00, 0xF4, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0x00, 0x00,
+    0x00, 0x00, 0xC4, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0x01, 0x00, 0x00, 0x00, 0x30, 0x00,
+    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01, 0x00,
+    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00, 0x7C, 0x00, 0x00, 0x00, 0x00, 0x00,
+    0x00, 0x00, 0x7C, 0x00, 0x00, 0x00, 0x18, 0x02, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0xF4, 0xFF,
+    0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0x00, 0x00, 0x00, 0x00, 0xA1, 0xD9, 0x13, 0x0B, 0x80, 0xBB,
+    0xFE, 0x3C, 0x00, 0x00, 0x00, 0x86, 0x00, 0x04, 0x00, 0x00, 0x00, 0x46, 0x75, 0x67, 0x17, 0x6D,
+    0x00, 0x40, 0x00, 0x01, 0x00, 0x00, 0x03, 0x62, 0x00, 0x00, 0x00, 0x64, 0x1B, 0x52, 0x4F, 0x4F,
+    0x54, 0x3A, 0x3A, 0x45, 0x78, 0x70, 0x65, 0x72, 0x69, 0x6D, 0x65, 0x6E, 0x74, 0x61, 0x6C, 0x3A,
+    0x3A, 0x52, 0x4E, 0x54, 0x75, 0x70, 0x6C, 0x65, 0x08, 0x6D, 0x79, 0x6E, 0x74, 0x75, 0x70, 0x6C,
+    0x65, 0x00, 0x40, 0x00, 0x00, 0x42, 0x00, 0x04, 0x00, 0x00, 0x00, 0x02, 0x00, 0x00, 0x00, 0x00,
+    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01, 0x16, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0xBA,
+    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0xBA, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x02, 0xB6,
+    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0xAC, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0xAC,
+    0xDC, 0x49, 0x5F, 0xD0, 0x14, 0x79, 0xAF, 0x1B, 0x00, 0x00, 0x00, 0x79, 0x00, 0x04, 0x00, 0x00,
+    0x00, 0x44, 0x75, 0x67, 0x17, 0x6D, 0x00, 0x35, 0x00, 0x01, 0x00, 0x00, 0x03, 0xE8, 0x00, 0x00,
+    0x00, 0x64, 0x00, 0x18, 0x74, 0x65, 0x73, 0x74, 0x5F, 0x6E, 0x74, 0x75, 0x70, 0x6C, 0x65, 0x5F,
+    0x6D, 0x69, 0x6E, 0x69, 0x6D, 0x61, 0x6C, 0x2E, 0x72, 0x6F, 0x6F, 0x74, 0x00, 0x00, 0x00, 0x00,
+    0x01, 0x00, 0x00, 0x00, 0x86, 0x00, 0x04, 0x00, 0x00, 0x00, 0x46, 0x75, 0x67, 0x17, 0x6D, 0x00,
+    0x40, 0x00, 0x01, 0x00, 0x00, 0x03, 0x62, 0x00, 0x00, 0x00, 0x64, 0x1B, 0x52, 0x4F, 0x4F, 0x54,
+    0x3A, 0x3A, 0x45, 0x78, 0x70, 0x65, 0x72, 0x69, 0x6D, 0x65, 0x6E, 0x74, 0x61, 0x6C, 0x3A, 0x3A,
+    0x52, 0x4E, 0x54, 0x75, 0x70, 0x6C, 0x65, 0x08, 0x6D, 0x79, 0x6E, 0x74, 0x75, 0x70, 0x6C, 0x65,
+    0x00, 0x00, 0x00, 0x01, 0xA3, 0x00, 0x04, 0x00, 0x00, 0x04, 0xF2, 0x75, 0x67, 0x17, 0x6D, 0x00,
+    0x40, 0x00, 0x01, 0x00, 0x00, 0x04, 0x61, 0x00, 0x00, 0x00, 0x64, 0x05, 0x54, 0x4C, 0x69, 0x73,
+    0x74, 0x0C, 0x53, 0x74, 0x72, 0x65, 0x61, 0x6D, 0x65, 0x72, 0x49, 0x6E, 0x66, 0x6F, 0x12, 0x44,
+    0x6F, 0x75, 0x62, 0x6C, 0x79, 0x20, 0x6C, 0x69, 0x6E, 0x6B, 0x65, 0x64, 0x20, 0x6C, 0x69, 0x73,
+    0x74, 0x5A, 0x4C, 0x08, 0x5A, 0x01, 0x00, 0xF2, 0x04, 0x00, 0x78, 0x01, 0xBD, 0x92, 0x4D, 0x4E,
+    0xC2, 0x40, 0x1C, 0xC5, 0x1F, 0x05, 0x13, 0x91, 0x8F, 0xAD, 0x1A, 0x36, 0x6E, 0xBD, 0x42, 0x57,
+    0x15, 0x83, 0x91, 0x44, 0x29, 0x42, 0xC5, 0x68, 0x82, 0x66, 0x80, 0x29, 0x94, 0x8F, 0x99, 0x66,
+    0xDA, 0x26, 0xB2, 0x63, 0xE7, 0x69, 0xBC, 0x84, 0x97, 0xD0, 0x53, 0x78, 0x05, 0xFD, 0x77, 0x24,
+    0x04, 0x12, 0x89, 0x68, 0x83, 0x2F, 0x99, 0x69, 0x3B, 0xED, 0xBC, 0x5F, 0xFB, 0x5E, 0x2D, 0x64,
+    0xDE, 0xB1, 0x83, 0x14, 0x48, 0x46, 0x3C, 0x91, 0x52, 0x16, 0x32, 0x6F, 0x1F, 0x24, 0xA7, 0x19,
+    0x2A, 0xCE, 0x26, 0x5C, 0x55, 0x85, 0x2B, 0x41, 0xAB, 0x2F, 0xC8, 0x5A, 0xC0, 0x31, 0x3D, 0xAE,
+    0x37, 0xA4, 0x69, 0x2E, 0x35, 0x6C, 0xDB, 0x31, 0xCD, 0xCA, 0xA3, 0xCF, 0x95, 0x37, 0xE1, 0x22,
+    0x64, 0x63, 0xD3, 0x6C, 0xD4, 0x9C, 0xC8, 0x1F, 0x73, 0xB4, 0xF3, 0xCF, 0x55, 0x32, 0xCC, 0xD0,
+    0xD6, 0x27, 0x6D, 0x68, 0x77, 0x86, 0x27, 0x4A, 0xB1, 0x69, 0x6C, 0x16, 0x21, 0xBD, 0xCA, 0xCD,
+    0xC5, 0x70, 0xF2, 0x8F, 0x56, 0xD8, 0x65, 0x16, 0x78, 0x5D, 0x67, 0xEA, 0xF3, 0xF8, 0xD6, 0x1D,
+    0x0C, 0x9A, 0x9D, 0xD8, 0x11, 0xA5, 0xC5, 0x6B, 0x00, 0x28, 0xB8, 0x2D, 0xAE, 0x02, 0x4F, 0x8A,
+    0x8A, 0x2F, 0xBB, 0x03, 0x5A, 0x40, 0x9E, 0x86, 0x11, 0x9F, 0xAC, 0x53, 0x31, 0x12, 0x81, 0xD7,
+    0x17, 0xBC, 0x77, 0x14, 0x0C, 0xA4, 0x0A, 0x2D, 0xA0, 0x33, 0x03, 0x5E, 0xE9, 0xF8, 0x33, 0xE5,
+    0x92, 0x0D, 0xA5, 0x8A, 0x8D, 0xB7, 0x4B, 0xF1, 0xC4, 0x3F, 0x50, 0xEA, 0x2C, 0xFC, 0x73, 0x62,
+    0x0F, 0xF3, 0xC4, 0x6E, 0x60, 0x58, 0xC0, 0x95, 0xEE, 0xE5, 0x70, 0xB9, 0x97, 0x9C, 0xDB, 0xE4,
+    0x7C, 0x74, 0xCE, 0x59, 0x8F, 0xEB, 0xBC, 0x8A, 0x00, 0x76, 0x69, 0xAC, 0x55, 0x61, 0xD1, 0xCA,
+    0x58, 0x8A, 0xBE, 0x05, 0xB0, 0xD9, 0x57, 0x29, 0xB7, 0x30, 0xE8, 0xAA, 0xF9, 0x5D, 0xF5, 0xB5,
+    0xF2, 0x34, 0xE4, 0x41, 0x12, 0xC8, 0xFD, 0x1C, 0xD2, 0xD2, 0x90, 0xBA, 0x86, 0x1C, 0x2C, 0x7F,
+    0xC7, 0x9E, 0x7B, 0xC1, 0x45, 0x12, 0xC2, 0x86, 0x49, 0x9D, 0x49, 0x19, 0x6E, 0x3D, 0xA9, 0x24,
+    0x90, 0xCD, 0x92, 0x4A, 0x42, 0x68, 0xCF, 0xBB, 0xB8, 0xD6, 0x5D, 0xD8, 0xBA, 0x8B, 0xFD, 0xE5,
+    0x2E, 0xB2, 0xEE, 0xE9, 0x80, 0x77, 0x47, 0x41, 0x34, 0x01, 0xE9, 0x97, 0x7F, 0x14, 0x3E, 0x01,
+    0x15, 0x3D, 0xC1, 0xCA, 0x00, 0x00, 0x00, 0x3F, 0x00, 0x04, 0x00, 0x00, 0x00, 0x0A, 0x75, 0x67,
+    0x17, 0x6D, 0x00, 0x35, 0x00, 0x01, 0x00, 0x00, 0x06, 0x04, 0x00, 0x00, 0x00, 0x64, 0x00, 0x18,
+    0x74, 0x65, 0x73, 0x74, 0x5F, 0x6E, 0x74, 0x75, 0x70, 0x6C, 0x65, 0x5F, 0x6D, 0x69, 0x6E, 0x69,
+    0x6D, 0x61, 0x6C, 0x2E, 0x72, 0x6F, 0x6F, 0x74, 0x00, 0x00, 0x01, 0x00, 0x00, 0x06, 0x43, 0x77,
+    0x35, 0x94, 0x00,
+]
+
+function test_io(obj, expected; kw...)
+    a = IOBuffer()
+    rnt_write(a, obj; kw...)
+    ours = take!(a)
+    @test ours == expected
+end
+
+@testset "RNTuple Writing - Internal" begin
+
+dummy_FileHeader = [
+    0x00, 0x00, 0x00, 0x64, 0x00, 0x00, 0x06, 0x43, 0x00, 0x00, 0x06, 0x04, 0x00, 0x00, 0x00, 0x3F,
+    0x00, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00, 0x54, 0x04, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x04,
+    0x61, 0x00, 0x00, 0x01, 0xA3, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+]
+test_io(UnROOT.Stubs.fileheader, dummy_FileHeader)
+
+dummy_tkey32_tfile = [
+    0x00, 0x00, 0x00, 0x90, 0x00, 0x04, 0x00, 0x00, 0x00, 0x56, 0x75, 0x67, 0x17, 0x6D, 0x00, 0x3A,
+    0x00, 0x01, 0x00, 0x00, 0x00, 0x64, 0x00, 0x00, 0x00, 0x00, 0x05, 0x54, 0x46, 0x69, 0x6C, 0x65,
+    0x18, 0x74, 0x65, 0x73, 0x74, 0x5F, 0x6E, 0x74, 0x75, 0x70, 0x6C, 0x65, 0x5F, 0x6D, 0x69, 0x6E,
+    0x69, 0x6D, 0x61, 0x6C, 0x2E, 0x72, 0x6F, 0x6F, 0x74, 0x00,
+]
+test_io(UnROOT.Stubs.tkey32_tfile, dummy_tkey32_tfile)
+
+dummy_tfile = [
+    0x18, 0x74, 0x65, 0x73, 0x74, 0x5F, 0x6E, 0x74, 0x75, 0x70, 0x6C, 0x65, 0x5F, 0x6D, 0x69, 0x6E,
+    0x69, 0x6D, 0x61, 0x6C, 0x2E, 0x72, 0x6F, 0x6F, 0x74, 0x00,
+]
+test_io(UnROOT.Stubs.tfile, dummy_tfile)
+
+dummy_tdirectory32 = [
+    0x00, 0x05, 0x75, 0x67, 0x17, 0x6D, 0x75, 0x67, 0x17, 0x6D, 0x00, 0x00, 0x00, 0x79, 0x00, 0x00,
+    0x00, 0x54, 0x00, 0x00, 0x00, 0x64, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x03, 0xE8,
+]
+test_io(UnROOT.Stubs.tdirectory32, dummy_tdirectory32)
+
+dummy_padding2 = [
+    0x00, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+]
+
+dummy_RBlob1 = [
+    0x00, 0x00, 0x00, 0xDC, 0x00, 0x04, 0x00, 0x00, 0x00, 0xBA, 0x75, 0x67, 0x17, 0x6D, 0x00, 0x22,
+    0x00, 0x01, 0x00, 0x00, 0x00, 0xF4, 0x00, 0x00, 0x00, 0x64, 0x05, 0x52, 0x42, 0x6C, 0x6F, 0x62,
+    0x00, 0x00,
+]
+test_io(UnROOT.Stubs.RBlob1, dummy_RBlob1)
+
+# ==================================== side tests begin ====================================
+    
+field_record = UnROOT.FieldRecord(zero(UInt32), zero(UInt32), zero(UInt32), zero(UInt16), zero(UInt16), 0, "one_uint", "std::uint32_t", "", "")
+dummy_field_record = [
+    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 
+    0x08, 0x00, 0x00, 0x00, 0x6F, 0x6E, 0x65, 0x5F, 0x75, 0x69, 0x6E, 0x74, 0x0D, 0x00, 0x00, 0x00, 
+    0x73, 0x74, 0x64, 0x3A, 0x3A, 0x75, 0x69, 0x6E, 0x74, 0x33, 0x32, 0x5F, 0x74, 0x00, 0x00, 0x00, 
+    0x00, 0x00, 0x00, 0x00, 0x00, 
+]
+test_io(field_record, dummy_field_record)
+
+column_record = UnROOT.ColumnRecord(0x14, 0x20, zero(UInt32), zero(UInt32), 0)
+dummy_column_record = [
+    0x14, 0x00, 0x20, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 
+]
+test_io(column_record, dummy_column_record)
+
+envelope_frame_field_record = Write_RNTupleListFrame([field_record])
+dummy_envelope_frame_field_record = [
+    0xB7, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0x01, 0x00, 0x00, 0x00, 0x3D, 0x00, 0x00, 0x00, 
+    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 
+    0x00, 0x00, 0x00, 0x00, 0x08, 0x00, 0x00, 0x00, 0x6F, 0x6E, 0x65, 0x5F, 0x75, 0x69, 0x6E, 0x74, 
+    0x0D, 0x00, 0x00, 0x00, 0x73, 0x74, 0x64, 0x3A, 0x3A, 0x75, 0x69, 0x6E, 0x74, 0x33, 0x32, 0x5F, 
+    0x74, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 
+]
+test_io(envelope_frame_field_record, dummy_envelope_frame_field_record)
+
+dummy_rnt_header_payload = [
+    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x08, 0x00, 0x00, 0x00, 0x6D, 0x79, 0x6E, 0x74, 
+    0x75, 0x70, 0x6C, 0x65, 0x00, 0x00, 0x00, 0x00, 0x0D, 0x00, 0x00, 0x00, 0x52, 0x4F, 0x4F, 0x54, 
+    0x20, 0x76, 0x36, 0x2E, 0x33, 0x33, 0x2E, 0x30, 0x31, 0xB7, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 
+    0xFF, 0x01, 0x00, 0x00, 0x00, 0x3D, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 
+    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x08, 0x00, 0x00, 
+    0x00, 0x6F, 0x6E, 0x65, 0x5F, 0x75, 0x69, 0x6E, 0x74, 0x0D, 0x00, 0x00, 0x00, 0x73, 0x74, 0x64, 
+    0x3A, 0x3A, 0x75, 0x69, 0x6E, 0x74, 0x33, 0x32, 0x5F, 0x74, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 
+    0x00, 0x00, 0xE0, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0x01, 0x00, 0x00, 0x00, 0x14, 0x00, 
+    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x14, 0x00, 0x20, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 
+    0x00, 0x00, 0xF4, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0x00, 0x00, 0x00, 0x00, 0xF4, 0xFF, 
+    0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0x00, 0x00, 0x00, 0x00, 
+]
+test_io(UnROOT.Stubs.rnt_header, dummy_rnt_header_payload; envelope=false)
+
+# ==================================== side tests end ====================================
+
+dummy_rnt_header = [
+    0x01, 0x00, 0xBA, 0x00, 0x00, 0x00, 0x00, 0x00, dummy_rnt_header_payload..., 0x28, 0x7E, 0xC6, 0x09, 0xC0, 0x59, 0xEC, 0x3D,
+]
+test_io(UnROOT.Stubs.rnt_header, dummy_rnt_header; envelope=true)
+
+dummy_RBlob2 = [
+    0x00, 0x00, 0x00, 0x26, 0x00, 0x04, 0x00, 0x00, 0x00, 0x04, 0x75, 0x67, 0x17, 0x6D, 0x00, 0x22,
+    0x00, 0x01, 0x00, 0x00, 0x01, 0xD0, 0x00, 0x00, 0x00, 0x64, 0x05, 0x52, 0x42, 0x6C, 0x6F, 0x62,
+    0x00, 0x00,
+]
+test_io(UnROOT.Stubs.RBlob2, dummy_RBlob2)
+
+dummy_RBlob3 = [
+    0x00, 0x00, 0x00, 0x9E, 0x00, 0x04, 0x00, 0x00, 0x00, 0x7C, 0x75, 0x67, 0x17, 0x6D, 0x00, 0x22,
+    0x00, 0x01, 0x00, 0x00, 0x01, 0xF6, 0x00, 0x00, 0x00, 0x64, 0x05, 0x52, 0x42, 0x6C, 0x6F, 0x62,
+    0x00, 0x00,
+]
+test_io(UnROOT.Stubs.RBlob3, dummy_RBlob3)
+
+# ================= side tests begin =================
+dummy_cluster_summary = [
+    0xDC, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0x01, 0x00, 0x00, 0x00, 0x18, 0x00, 0x00, 0x00, 
+    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00, 
+    0x00, 0x00, 0x00, 0x00, 
+]
+test_io(UnROOT.Stubs.cluster_summary, dummy_cluster_summary)
+
+# > https://github.com/root-project/root/blob/1a854602e42d4493f56a26e35e19bdf23b7d0933/tree/ntuple/v7/doc/specifications.md?plain=1#L672
+# > The inner list is followed by a 64bit unsigned integer element offset and the 32bit compression settings
+dummy_inner_list_frame = [
+    0xD8, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0x01, 0x00, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00, 
+    0x04, 0x00, 0x00, 0x00, 0xF2, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 
+    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 
+]
+
+inner_list_frame = UnROOT.RNTuplePageInnerList([
+    PageDescription(0x00000001, UnROOT.Locator(4, 0x00000000000001f2, )),
+])
+test_io(inner_list_frame, dummy_inner_list_frame)
+
+dummy_pagelink_noenvelope = [
+    0x28, 0x7E, 0xC6, 0x09, 0xC0, 0x59, 0xEC, 0x3D,
+    0xDC, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0x01, 0x00, 0x00, 0x00, 0x18, 0x00, 0x00, 0x00,
+    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00,
+    0x00, 0x00, 0x00, 0x00, 0xC0, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0x01, 0x00, 0x00, 0x00,
+    0xCC, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0x01, 0x00, 0x00, 0x00, 0xD8, 0xFF, 0xFF, 0xFF,
+    0xFF, 0xFF, 0xFF, 0xFF, 0x01, 0x00, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00, 0x04, 0x00, 0x00, 0x00,
+    0xF2, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+    0x00, 0x00, 0x00, 0x00
+]
+test_io(UnROOT.Stubs.pagelink, dummy_pagelink_noenvelope; envelope=false)
+# ================= side tests end =================
+
+
+dummy_pagelink = [
+    0x03, 0x00, 0x7C, 0x00, 0x00, 0x00, 0x00, 0x00, 0x28, 0x7E, 0xC6, 0x09, 0xC0, 0x59, 0xEC, 0x3D,
+    0xDC, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0x01, 0x00, 0x00, 0x00, 0x18, 0x00, 0x00, 0x00,
+    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00,
+    0x00, 0x00, 0x00, 0x00, 0xC0, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0x01, 0x00, 0x00, 0x00,
+    0xCC, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0x01, 0x00, 0x00, 0x00, 0xD8, 0xFF, 0xFF, 0xFF,
+    0xFF, 0xFF, 0xFF, 0xFF, 0x01, 0x00, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00, 0x04, 0x00, 0x00, 0x00,
+    0xF2, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+    0x00, 0x00, 0x00, 0x00, 0x1C, 0xA0, 0xDF, 0x2E, 0x25, 0x1E, 0x55, 0x4C,
+]
+test_io(UnROOT.Stubs.pagelink, dummy_pagelink)
+
+dummy_RBlob4 = [
+    0x00, 0x00, 0x00, 0xCE, 0x00, 0x04, 0x00, 0x00, 0x00, 0xAC, 0x75, 0x67, 0x17, 0x6D, 0x00, 0x22,
+    0x00, 0x01, 0x00, 0x00, 0x02, 0x94, 0x00, 0x00, 0x00, 0x64, 0x05, 0x52, 0x42, 0x6C, 0x6F, 0x62,
+    0x00, 0x00,
+]
+test_io(UnROOT.Stubs.RBlob4, dummy_RBlob4)
+
+dummy_rnt_footer = [
+    0x02, 0x00, 0xAC, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+    0x28, 0x7E, 0xC6, 0x09, 0xC0, 0x59, 0xEC, 0x3D, 0x38, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+    0xF4, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0x00, 0x00, 0x00, 0x00, 0xF4, 0xFF, 0xFF, 0xFF,
+    0xFF, 0xFF, 0xFF, 0xFF, 0x00, 0x00, 0x00, 0x00, 0xF4, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
+    0x00, 0x00, 0x00, 0x00, 0xF4, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0x00, 0x00, 0x00, 0x00,
+    0xF4, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0x00, 0x00, 0x00, 0x00, 0xC4, 0xFF, 0xFF, 0xFF,
+    0xFF, 0xFF, 0xFF, 0xFF, 0x01, 0x00, 0x00, 0x00, 0x30, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+    0x01, 0x00, 0x00, 0x00, 0x7C, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x7C, 0x00, 0x00, 0x00,
+    0x18, 0x02, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0xF4, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
+    0x00, 0x00, 0x00, 0x00, 0xA1, 0xD9, 0x13, 0x0B, 0x80, 0xBB, 0xFE, 0x3C,
+]
+test_io(UnROOT.Stubs.rnt_footer, dummy_rnt_footer)
+
+dummy_tkey32_anchor = [
+    0x00, 0x00, 0x00, 0x86, 0x00, 0x04, 0x00, 0x00, 0x00, 0x46, 0x75, 0x67, 0x17, 0x6D, 0x00, 0x40,
+    0x00, 0x01, 0x00, 0x00, 0x03, 0x62, 0x00, 0x00, 0x00, 0x64, 0x1B, 0x52, 0x4F, 0x4F, 0x54, 0x3A,
+    0x3A, 0x45, 0x78, 0x70, 0x65, 0x72, 0x69, 0x6D, 0x65, 0x6E, 0x74, 0x61, 0x6C, 0x3A, 0x3A, 0x52,
+    0x4E, 0x54, 0x75, 0x70, 0x6C, 0x65, 0x08, 0x6D, 0x79, 0x6E, 0x74, 0x75, 0x70, 0x6C, 0x65, 0x00,
+]
+
+dummy_rnt_anchor = [
+    0x00, 0x00, 0x00, 0x02, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01, 0x16,
+    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0xBA, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0xBA,
+    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x02, 0xB6, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0xAC,
+    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0xAC, 0xDC, 0x49, 0x5F, 0xD0, 0x14, 0x79, 0xAF, 0x1B,
+]
+test_io(UnROOT.Stubs.rnt_anchor, dummy_rnt_anchor)
+
+dummy_tkey32_TDirectory = [
+    0x00, 0x00, 0x00, 0x79, 0x00, 0x04, 0x00, 0x00, 0x00, 0x44, 0x75, 0x67, 0x17, 0x6D, 0x00, 0x35,
+    0x00, 0x01, 0x00, 0x00, 0x03, 0xE8, 0x00, 0x00, 0x00, 0x64, 0x00, 0x18, 0x74, 0x65, 0x73, 0x74,
+    0x5F, 0x6E, 0x74, 0x75, 0x70, 0x6C, 0x65, 0x5F, 0x6D, 0x69, 0x6E, 0x69, 0x6D, 0x61, 0x6C, 0x2E,
+    0x72, 0x6F, 0x6F, 0x74, 0x00,
+]
+test_io(UnROOT.Stubs.tkey32_TDirectory, dummy_tkey32_TDirectory)
+
+dummy_tkey32_TStreamerInfo = [
+    0x00, 0x00, 0x01, 0xA3, 0x00, 0x04, 0x00, 0x00, 0x04, 0xF2, 0x75, 0x67, 0x17, 0x6D, 0x00, 0x40,
+    0x00, 0x01, 0x00, 0x00, 0x04, 0x61, 0x00, 0x00, 0x00, 0x64, 0x05, 0x54, 0x4C, 0x69, 0x73, 0x74,
+    0x0C, 0x53, 0x74, 0x72, 0x65, 0x61, 0x6D, 0x65, 0x72, 0x49, 0x6E, 0x66, 0x6F, 0x12, 0x44, 0x6F,
+    0x75, 0x62, 0x6C, 0x79, 0x20, 0x6C, 0x69, 0x6E, 0x6B, 0x65, 0x64, 0x20, 0x6C, 0x69, 0x73, 0x74,
+]
+test_io(UnROOT.Stubs.tkey32_TStreamerInfo, dummy_tkey32_TStreamerInfo)
+
+
+MINE = [
+    UnROOT.Stubs.file_preamble;
+    dummy_FileHeader; UnROOT.Stubs.dummy_padding1;
+    dummy_tkey32_tfile; dummy_tfile;
+    dummy_tdirectory32; UnROOT.Stubs.dummy_padding2;
+    dummy_RBlob1; dummy_rnt_header;
+    dummy_RBlob2; UnROOT.Stubs.page1;
+    dummy_RBlob3; dummy_pagelink;
+    dummy_RBlob4; dummy_rnt_footer;
+    dummy_tkey32_anchor; UnROOT.Stubs.magic_6bytes; dummy_rnt_anchor;
+    dummy_tkey32_TDirectory; UnROOT.Stubs.n_keys; dummy_tkey32_anchor;
+    dummy_tkey32_TStreamerInfo; UnROOT.Stubs.tsreamerinfo_compressed;
+    UnROOT.Stubs.tfile_end
+]
+
+mytable = Dict("one_uint" => UInt32[0xcececece])
+myio = IOBuffer()
+UnROOT.write_rntuple(myio, mytable; rntuple_name="myntuple")
+@test MINE == REFERENCE_BYTES
+mio = take!(myio)
+@test MINE == mio
+
+for _ = 1:100
+    newtable = Dict(randstring(rand(2:10)) => rand(UInt32, rand(1:1000)))
+    newio = IOBuffer()
+    UnROOT.write_rntuple(newio, newtable)
+    nio = take!(newio)
+
+    if isfile("a.root")
+        rm("a.root")
+    end
+
+    open("a.root", "w") do f
+        write(f, nio)
+    end
+
+    rntuple_name = "myntuple"
+    t = LazyTree("a.root", rntuple_name)
+    @test sort(names(t)) == sort(collect(keys(newtable)))
+    @test only(columntable(t)) == only(columntable(newtable))
+
+end
+end
diff --git a/test/runtests.jl b/test/runtests.jl
index 0221f962..d4be502c 100644
--- a/test/runtests.jl
+++ b/test/runtests.jl
@@ -28,5 +28,6 @@ nthreads == 1 && @warn "Running on a single thread. Please re-run the test suite
 
     if VERSION >= v"1.9"
         include("rntuple.jl")
+        include("./RNTupleWriting/lowlevel.jl")
     end
 end