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

Annotations declare readOnlyHint=true, indicating a non-destructive read operation. The description adds detail about the return fields (reason phrase, description, category, cacheability, RFC) and behavior for keyword queries (returns closest match plus alternatives). This goes beyond the basic annotation but doesn't describe potential edge cases such as invalid queries or ambiguous matches. Given the annotation covers safety, a 3 is appropriate.

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?

The description is concise, covering purpose, return fields, behavior, and keyword handling in three sentences with no redundancy. It is front-loaded with the core purpose first, then elaboration.

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?

The tool has an output schema which likely describes the return structure, so the description doesn't need to explain return values. The description covers query types and return fields, which is sufficient for an agent to call it correctly. It doesn't cover error cases (e.g., unknown code), but the output schema may handle that. Overall, nearly complete.

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%, with the query parameter fully described in the schema ('Numeric status code... or descriptive keyword...'). The description adds examples of keywords and clarifies the output, but does not add significant new information beyond the schema. Baseline 3 is appropriate since the schema already handles parameter documentation.

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 clearly states the tool's purpose: looking up HTTP status codes by number or keyword. It specifically lists the resource (HTTP status codes) and the verb (look up), and details what is returned. It is easily distinguishable from siblings which cover constants, elements, geo, timezone, etc.

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?

The description explains when to use this tool: when the user wants information about an HTTP status code by number or keyword. It does not explicitly mention that for other reference lookups (e.g., constants, elements) the user should use sibling tools, but this is implicit from the sibling names and the scope. No exclusions are stated, but the context is clear.

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