diff --git a/tools/bump_in_Base.jl b/tools/bump_in_Base.jl
new file mode 100644
index 00000000..c9ca7473
--- /dev/null
+++ b/tools/bump_in_Base.jl
@@ -0,0 +1,75 @@
+function find_checksum_files(checksum_dir)
+    filter(readdir(checksum_dir, join=true)) do path
+        occursin(r"^JuliaSyntax-", basename(path))
+    end
+end
+
+function bump_in_Base(julia_dir, juliasyntax_dir, juliasyntax_branch_or_commit)
+    julia_git_dir = joinpath(julia_dir, ".git")
+    JuliaSyntax_git_dir = joinpath(juliasyntax_dir, ".git")
+    if !isdir(julia_git_dir)
+        @error "Julia .git directory not found" julia_git_dir
+        return 1
+    end
+    if !isdir(JuliaSyntax_git_dir)
+        @error "JuliaSyntax .git directory not found" JuliaSyntax_git_dir
+        return 1
+    end
+
+    @info "Vendoring JuliaSyntax into Base" julia_dir juliasyntax_branch_or_commit
+
+    remote_containing_branches = filter(b->occursin(r"^origin/(main|release-.*)$", b),
+        strip.(split(
+            read(`git --git-dir=$JuliaSyntax_git_dir branch -r --contains $juliasyntax_branch_or_commit`, String),
+            '\n', keepempty=false)))
+    if isempty(remote_containing_branches)
+        @warn "No remote main or release branches contain the given commit. This is ok for testing, but is otherwise an error." juliasyntax_branch_or_commit
+    else
+        @info "Given commit is accessible on remote branch" remote_containing_branches
+    end
+
+    commit_sha = strip(String(read(`git --git-dir=$JuliaSyntax_git_dir show -s --pretty=tformat:%H $juliasyntax_branch_or_commit`)))
+
+    cd(julia_dir) do
+        status = read(`git status --porcelain --untracked-files=no`, String)
+        if status != ""
+            @error "Julia git directory contains uncommitted changes" status=Text(status)
+            return 1
+        end
+
+        verfile_path = joinpath("deps", "JuliaSyntax.version")
+        @info "Updating JuliaSyntax.version" verfile_path
+        write(verfile_path, replace(read(verfile_path, String), r"JULIASYNTAX_SHA1.*"=>"JULIASYNTAX_SHA1 = "*commit_sha))
+        run(`git add $verfile_path`)
+
+        @info "Updating JuliaSyntax checksums"
+        deps_dir = "deps"
+        checksum_dir = joinpath(deps_dir, "checksums")
+        old_checksum_paths = find_checksum_files(checksum_dir)
+        if !isempty(old_checksum_paths)
+            run(`git rm -rf $old_checksum_paths`)
+        end
+        run(`make -C $deps_dir`)
+        run(`git add $(find_checksum_files(checksum_dir))`)
+
+        # Force rebuild of Base to include the newly vendored JuliaSyntax next time Julia is built.
+        # (TODO: fix the Makefile instead?)
+        touch("base/Base.jl")
+
+        @info "JuliaSyntax version updated. You can now test or commit the following changes"
+        run(`git diff --cached`)
+    end
+
+    return 0
+end
+
+if !isinteractive()
+    if length(ARGS) != 2
+        println("Usage: bump_in_Base.jl \$julia_dir \$juliasyntax_branch_or_commit")
+        exit(1)
+    else
+        juliasyntax_dir = dirname(@__DIR__)
+        exit(bump_in_Base(ARGS[1], juliasyntax_dir, ARGS[2]))
+    end
+end
+