Content-Language Inspect

Parse and diagnose HTTP headers and routing signals in your browser. No input is sent to a server. Use it for first-pass observation-gap troubleshooting.

Status

Runs in your browser. No input is sent to a server. Use this as a first-pass diagnostic step.

How to use

Paste Content-Language or Response Headers and click “Parse”. It summarizes the returned language tags.

Notes (this tool)

  • Accepts Content-Language: header lines (multi-line paste is OK).
  • If multiple languages are listed, they are shown as a list.

About this page

What does this tool do?

Split Content-Language to list returned language tags (ja/en/zh-Hans, etc.).

Useful for checking mismatches between expected and actual response language.

Basics (vs Accept-Language)

  • Accept-Language is preference; Content-Language is what was returned.
  • If the same URL varies by language, Vary: Accept-Language is required.
  • Splitting languages by URL can be more stable.

How to read language tags

  • ja: Japanese
  • en-US: English (United States)
  • zh-Hans: Chinese (Simplified)

Input examples

  • Content-Language: ja
  • Content-Language: en-US, en
  • Paste full Response Headers

Caching and Vary

If Content-Language varies, missing Vary: Accept-Language can cause cache mixing.

Common pitfalls

  • Missing Content-Language (unclear language)
  • Mismatch between URL and Content-Language (e.g., /en/ but ja)
  • Missing Vary causes mixed languages in CDN cache

Debugging workflow (recommended)

  • Extract Content-Language via Response Headers Parser
  • Summarize returned language with this tool
  • Check request preferences with Accept-Language Inspect
  • Accept-Language Inspect
  • Vary Inspect
  • Response Headers Parser

What this tool does

  • Parse Content-Language and list tags
  • Highlight mismatch checks

Operational notes

  • Intermediaries may rewrite headers. Compare captures from equivalent points.
  • Confirm final decisions with server logs and configuration such as trusted proxy and routing.

Referenced specs

  • RFC 9110 (HTTP Semantics)
  • RFC 5646 (Language Tags)
  • MDN: Content-Language

FAQ

What if Content-Language is missing?

It’s optional, but you lose a clear signal. It’s helpful for multilingual pages.

Can Content-Language list multiple languages?

Yes, it can list multiple languages for mixed-language content.

References

  1. RFC 9110
  2. RFC 5646
  3. MDN: Content-Language
  4. MDN: Accept-Language

These links are generated from site_map rules in recommended diagnostic order.

  1. Accept-Charset Inspect — Parse Accept-Charset and inspect charset preferences
  2. Accept-Language Inspect — Parse Accept-Language and inspect language priority
  3. Accept Header Builder — Build Accept-family headers by use case

Language/Locale

Compare Accept headers with Content-Language to debug negotiation mismatches