diff --git a/testing/web-platform/tests/fetch/content-length/parsing.window.js b/testing/web-platform/tests/fetch/content-length/parsing.window.js
new file mode 100644
index 0000000000000..0e1654defab47
--- /dev/null
+++ b/testing/web-platform/tests/fetch/content-length/parsing.window.js
@@ -0,0 +1,161 @@
+promise_test
+(
+(
+)
+=
+>
+{
+return
+fetch
+(
+"
+resources
+/
+content
+-
+lengths
+.
+json
+"
+)
+.
+then
+(
+res
+=
+>
+res
+.
+json
+(
+)
+)
+.
+then
+(
+runTests
+)
+;
+}
+"
+Loading
+JSON
+"
+)
+;
+function
+runTests
+(
+testUnits
+)
+{
+testUnits
+.
+forEach
+(
+testUnit
+=
+>
+{
+const
+input
+=
+encodeURIComponent
+(
+testUnit
+.
+input
+)
+;
+promise_test
+(
+t
+=
+>
+{
+const
+result
+=
+fetch
+(
+"
+resources
+/
+content
+-
+length
+.
+py
+?
+length
+=
+"
++
+input
+)
+;
+if
+(
+testUnit
+.
+output
+=
+=
+=
+null
+)
+{
+return
+promise_rejects_js
+(
+t
+TypeError
+result
+)
+;
+}
+else
+{
+return
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+.
+then
+(
+res
+=
+>
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+.
+text
+(
+)
+)
+.
+then
+(
+text
+=
+>
+{
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+(
+text
+.
+length
+testUnit
+.
+output
+)
+;
+}
+)
+;
+}
+}
+input
+)
+;
+}
+)
+;
+}
diff --git a/testing/web-platform/tests/fetch/content-length/resources/content-length.py b/testing/web-platform/tests/fetch/content-length/resources/content-length.py
new file mode 100644
index 0000000000000..733d020f396b6
--- /dev/null
+++ b/testing/web-platform/tests/fetch/content-length/resources/content-length.py
@@ -0,0 +1,121 @@
+def
+main
+(
+request
+response
+)
+:
+    
+response
+.
+add_required_headers
+=
+False
+    
+output
+=
+b
+"
+HTTP
+/
+1
+.
+1
+200
+OK
+\
+r
+\
+n
+"
+    
+output
++
+=
+b
+"
+Content
+-
+Type
+:
+text
+/
+plain
+;
+charset
+=
+UTF
+-
+8
+\
+r
+\
+n
+"
+    
+output
++
+=
+request
+.
+GET
+.
+first
+(
+b
+"
+length
+"
+)
++
+b
+"
+\
+r
+\
+n
+"
+    
+output
++
+=
+b
+"
+\
+r
+\
+n
+"
+    
+output
++
+=
+b
+"
+Fact
+:
+this
+is
+really
+forty
+-
+two
+bytes
+long
+.
+"
+    
+response
+.
+writer
+.
+write
+(
+output
+)
+    
+response
+.
+close_connection
+=
+True
diff --git a/testing/web-platform/tests/fetch/content-length/resources/content-lengths.json b/testing/web-platform/tests/fetch/content-length/resources/content-lengths.json
new file mode 100644
index 0000000000000..d476426a2f655
--- /dev/null
+++ b/testing/web-platform/tests/fetch/content-length/resources/content-lengths.json
@@ -0,0 +1,676 @@
+[
+{
+"
+input
+"
+:
+"
+Content
+-
+Length
+:
+42
+"
+"
+output
+"
+:
+42
+}
+{
+"
+input
+"
+:
+"
+Content
+-
+Length
+:
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+"
+"
+output
+"
+:
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+}
+{
+"
+input
+"
+:
+"
+Content
+-
+Length
+:
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+\
+r
+\
+nContent
+-
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+"
+"
+output
+"
+:
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+}
+{
+"
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+"
+:
+"
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+-
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+:
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+\
+r
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+nContent
+-
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+:
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+"
+"
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+:
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+}
+{
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+input
+"
+:
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+-
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+"
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+"
+:
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+}
+{
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+input
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+:
+"
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+-
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+"
+"
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+"
+:
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+}
+{
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+input
+"
+:
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+-
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+:
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+}
+{
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+"
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+:
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+}
+{
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+"
+:
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+Length
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+"
+output
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+:
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+}
+{
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+:
+"
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+-
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+"
+"
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+:
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+}
+{
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+}
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+"
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+:
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+}
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+-
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+-
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+"
+output
+"
+:
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+}
+{
+"
+input
+"
+:
+"
+Content
+-
+Length
+:
+aaaah
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+r
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+nContent
+-
+Length
+:
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+"
+"
+output
+"
+:
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+}
+{
+"
+input
+"
+:
+"
+Content
+-
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+"
+"
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+"
+:
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+}
+{
+"
+input
+"
+:
+"
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+-
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+:
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+-
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+"
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+"
+:
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+}
+{
+"
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+"
+:
+"
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+-
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+"
+"
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+"
+:
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+}
+{
+"
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+"
+:
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+-
+Length
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+"
+"
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+"
+:
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+}
+{
+"
+input
+"
+:
+"
+Content
+-
+Length
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+"
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+"
+:
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+}
+{
+"
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+"
+:
+"
+Content
+-
+Length
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+"
+"
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+"
+:
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+}
+{
+"
+input
+"
+:
+"
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+-
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+:
+-
+1
+"
+"
+output
+"
+:
+42
+}
+{
+"
+input
+"
+:
+"
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+-
+Length
+:
+0x20
+"
+"
+output
+"
+:
+42
+}
+{
+"
+input
+"
+:
+"
+Content
+-
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+:
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+"
+"
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+"
+:
+30
+}
+{
+"
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+"
+:
+"
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+-
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+:
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+\
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+\
+nContent
+-
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+:
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+"
+"
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+"
+:
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+}
+{
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+-
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+:
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+"
+"
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+"
+:
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+}
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+"
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+"
+:
+"
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+-
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+:
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+"
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+\
+"
+"
+"
+output
+"
+:
+42
+}
+{
+"
+input
+"
+:
+"
+Content
+-
+Length
+:
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+\
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+\
+nContent
+-
+Length
+:
+\
+r
+\
+nContent
+-
+Length
+:
+30
+"
+"
+output
+"
+:
+null
+}
+{
+"
+input
+"
+:
+"
+Content
+-
+Length
+:
+"
+"
+output
+"
+:
+42
+}
+]
diff --git a/testing/web-platform/tests/fetch/content-length/too-long.window.js b/testing/web-platform/tests/fetch/content-length/too-long.window.js
new file mode 100644
index 0000000000000..65c60b6d98720
--- /dev/null
+++ b/testing/web-platform/tests/fetch/content-length/too-long.window.js
@@ -0,0 +1,65 @@
+promise_test
+(
+async
+t
+=
+>
+{
+const
+result
+=
+await
+fetch
+(
+resources
+/
+content
+-
+length
+.
+py
+?
+length
+=
+{
+encodeURIComponent
+(
+"
+Content
+-
+Length
+:
+50
+"
+)
+}
+)
+;
+await
+promise_rejects_js
+(
+t
+TypeError
+result
+.
+text
+(
+)
+)
+;
+}
+"
+Content
+-
+Length
+header
+value
+of
+network
+response
+exceeds
+response
+body
+"
+)
+;