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Measure HTTP

facts.measure.http

Read-only

Make one HTTP request and record raw status, headers, body, time, and connected IP from the server's network position. Returns the observation without judging success or validating responses.

Instructions

Make one HTTP request and return the raw status, headers and body, with the time it was observed and the IP actually connected to. Measures from the server's network position. It does NOT judge the result: a 500 received cleanly is a successful observation (ok:true, http_status 500). It does not check the status against an expectation, does not validate the body, does not retry, and does not follow redirects unless asked.

Input Schema

Name	Required	Description	Default
`url`	Yes	Absolute URL. Subject to the network policy.
`body`	No	Request body. An object or array is serialized to JSON, with content-type application/json if absent; a string is sent as is.
`method`	No	HTTP method.	GET
`headers`	No	Request headers. Sent intact; redacted in the output and on disk.
`project`	Yes	Project this observation belongs to.
`timeout_ms`	No	Total timeout.
`max_body_bytes`	No	Body cap. On exceeding it the body is truncated and a warning is emitted.
`follow_redirects`	No	When false, a 302 is returned as a 302. Each hop is revalidated by the policy.

Output Schema

Name	Required	Description
`ok`	Yes	Whether the observation could be taken. NOT a judgement about what was observed: a cleanly received HTTP 500 is ok:true.
`data`	Yes	The raw observation, or null when error is set.
`tool`	Yes	Full tool name.
`error`	Yes	What prevented observing, if anything.
`target`	Yes	Effective arguments, redacted.
`project`	Yes	The normalized project.
`warnings`	Yes	Non-fatal notices.
`age_basis`	Yes	Which clock the age came from.
`request_id`	Yes	The request that produced it.
`age_seconds`	Yes	Seconds since observed_at.
`duration_ms`	Yes	How long the observation took.
`observed_at`	Yes	ISO 8601 with offset.
`observation_id`	Yes	Citable id of this observation.

Schema Changelog

Changes observed during successful MCP inspections.

First observedv0.3.0Oct 21, 2026

TDQS

A4.4/5.0

Behavior5/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

With readOnlyHint/openWorldHint already covering safety, the description still adds substantial behavioral context: no retry, no body validation, no status-checking, no redirect following unless asked, and the counterintuitive ok:true-with-500 semantics. This is exactly the kind of non-obvious contract an agent needs.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Three sentences, front-loaded with the core action and return payload, then the non-judgment semantics. Slight redundancy in the negative list ('does not check the status', 'does not validate', 'does not retry') but every clause carries distinct meaning.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness5/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

With an output schema present, the description needn't explain return values, and it still describes the observation envelope (ok flag, http_status, observed time, IP). Combined with a fully documented 8-parameter schema, nothing needed to invoke it correctly is missing.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, so the schema already documents every parameter including body serialization, redaction, truncation, and redirect revalidation. The description only echoes follow-redirect behavior and adds no syntax or format detail beyond the schema.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

Names a concrete verb and resource ('Make one HTTP request') and enumerates exactly what is returned (status, headers, body, observation time, connected IP). The phrase 'Measures from the server's network position' cleanly separates it from the sibling facts.measure.ws and from any client-side fetch.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines4/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The 'does NOT judge the result' paragraph effectively defines the boundary against an assertion tool (facts.recall.assert): this tool observes, it does not evaluate an expectation. No sibling is named explicitly and no exclusion is given for facts.measure.ws, so it falls short of a 5.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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