Look up an HTTP status code: what it means, what the client must do, whether it is retryable, whether it is safe to replay, the defining RFC and the common causes. ($0.003 per call)
| Name | Required | Description | Default |
|---|---|---|---|
| code | Yes | status code, e.g. 429 | |
| detail | No | summary = name and class only; decision = what the client should do | full |
Changes observed during successful MCP inspections.
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description carries the full burden, and it does reasonably well: it discloses the returned facets and adds non-obvious cost context ("$0.003 per call"). It does not state that the lookup is read-only or what happens for unknown/non-standard codes, which is the main remaining gap.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Is the description appropriately sized, front-loaded, and free of redundancy?
A single front-loaded sentence with a tight colon-separated list; the resource is named first and the payoff is immediate. The enumerative list is slightly long but each item corresponds to a distinct return field, so little is wasted.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
There is no output schema, so the description must convey the return surface — and it does, enumerating the answer components (meaning, client action, retryable, replay-safe, RFC, causes). Combined with the schema's detail enum, an agent has enough to call it correctly; only edge-case behavior for invalid codes is missing.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
Schema description coverage is 100%, so both parameters (code, detail) are already documented in the schema, including the detail enum levels. The description adds no syntax, default behavior, or format information beyond what the schema provides, so the baseline 3 applies.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Does the description clearly state what the tool does and how it differs from similar tools?
The description gives a specific verb+resource ("Look up an HTTP status code") and enumerates the exact facets returned: meaning, required client action, retryability, replay safety, RFC, and common causes. It clearly distinguishes the tool from vague neighbors, though it never names the closest siblings (retry_advice, status_for_situation) to explain how it differs.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Does the description explain when to use this tool, when not to, or what alternatives exist?
Usage is only implied — "look up an HTTP status code" makes the trigger obvious, but there is no explicit when-to-use, when-not-to-use, or alternative routing. A sibling like status_for_situation or retry_advice overlaps in domain, and the description gives no guidance on when to pick this tool instead.
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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