HTTP 431 header-fields-too-large
https://agent-observatory-sensor.nolimit-observatory.workers.dev/s/http-431/mcp ↗
Description
Meaning of HTTP 431.
What our measurements say
HTTP 431 header-fields-too-large is a remote MCP server published at agent-observatory-sensor.nolimit-observatory.workers.dev. It has been probed 6 times since 9/12/2026. It answered in 6 of them (100.0%), a near-uninterrupted record. Median response time is 36 ms, placing it among the faster endpoints. It exposes a broad tool surface of 30 tools. On the protocol side it still runs 2025-11-25 and has not moved to the newer spec.
Agent readability score
Can an LLM agent pick the right tool here — names, descriptions and parameter clarity are assessed.
Agent readability score
Agent readability score
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| Run | Era | Modern | ms | Legacy | ms | Versions |
|---|---|---|---|---|---|---|
| 2026-09-13 01:33:33 | Legacy | 404 | 36 | 200 | 33 | 2025-03-26 |
| 2026-09-12 23:31:36 | Legacy | 404 | 35 | 200 | 36 | 2025-03-26 |
| 2026-09-12 21:29:15 | Legacy | 404 | 36 | 200 | 34 | 2025-03-26 |
| 2026-09-12 19:27:29 | Legacy | 404 | 34 | 200 | 39 | 2025-03-26 |
| 2026-09-12 17:24:09 | Legacy | 404 | 41 | 200 | 40 | 2025-03-26 |
| 2026-09-12 15:21:42 | Legacy | 404 | 40 | 200 | 35 | 2025-03-26 |
Schema compliance
tools/list structure, inputSchema validity, and a functional smoke test — the components of the 0-100 score.
- tools/list schema valid
- inputSchema is valid JSON Schema
- Smoke test not run this round
- Cold-start: cold 35ms → warm 35ms (penalty 0ms)
Tools
Tools the server advertised in the latest measurement — measured, not catalog-claimed.
http-431Meaning of HTTP 431.
zonestringjsonstringurlstringhoststringcitystringquerystringpathstringrefstringfeedstring
utc-timeCurrent UTC timestamp.
zonestringjsonstringurlstringhoststringcitystringquerystringpathstringrefstringfeedstring
timezoneCurrent time in a named IANA timezone.
zonestringjsonstringurlstringhoststringcitystringquerystringpathstringrefstringfeedstring
validate-jsonCheck whether a body is valid JSON. The body is discarded.
zonestringjsonstringurlstringhoststringcitystringquerystringpathstringrefstringfeedstring
normalize-urlReturn origin, host, and path for a URL. Query and fragment are dropped.
zonestringjsonstringurlstringhoststringcitystringquerystringpathstringrefstringfeedstring
inspect-robotsFetch a public robots.txt and return group counts only.
zonestringjsonstringurlstringhoststringcitystringquerystringpathstringrefstringfeedstring
domain-shapeSplit a hostname into labels without WHOIS or ownership data.
zonestringjsonstringurlstringhoststringcitystringquerystringpathstringrefstringfeedstring
citationReturn host, scheme, and HTTP status for a URL. Page content is not stored.
zonestringjsonstringurlstringhoststringcitystringquerystringpathstringrefstringfeedstring
compatibilityShow how this request is classified. No identifiers are retained.
zonestringjsonstringurlstringhoststringcitystringquerystringpathstringrefstringfeedstring
status-catalogShort catalog of common HTTP status codes.
zonestringjsonstringurlstringhoststringcitystringquerystringpathstringrefstringfeedstring
iana-zonesCommon IANA timezone names for clock calls.
zonestringjsonstringurlstringhoststringcitystringquerystringpathstringrefstringfeedstring
web-fetchHTTP status and content type for a public URL. Body discarded.
zonestringjsonstringurlstringhoststringcitystringquerystringpathstringrefstringfeedstring
Availability history
Each block is one measurement round. Green: working response. Amber: responded but the server was returning errors (5xx). Red: no response at all.
Era history
Each cell is one probe run. Faded cells are incomplete probes — one leg did not answer, so the era is inconclusive.
Response time history
The two probe legs separately: modern server/discover and legacy initialize.
Event log
Derived by comparing consecutive probes — changes in era, protocol version, build and reachability.
- Added to watch — era: Legacy
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[](https://mcpmetrics.io/servers/io-github-sadri-dridi-http-431)<a href="https://mcpmetrics.io/servers/io-github-sadri-dridi-http-431"><img src="https://mcpmetrics.io/badge/io.github.sadri-dridi/http-431/era.svg" alt="mcpmetrics"></a>You are seeing the last 7 days. Sign up for the full history. Which check failed and why is in the dashboard.
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