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

With no annotations provided, the description carries the burden of behavioral disclosure. It explicitly states the output format (reason phrase and short description) and positions the tool for debugging/API responses. While it doesn't explicitly mention side-effect-free read-only behavior, the wording 'Explain... by returning' implies no mutation, and the exclusions clarify boundaries. A small addition about handling unknown codes would make it a 5.

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 well-structured with an opening sentence, a Use when list, and a Do not use list. Every line adds value, and the formatting makes it easy for an agent to scan and apply. No filler or redundancy.

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?

For a simple one-parameter lookup tool, the description is nearly complete. It defines the input, explains the output, and provides usage boundaries. It lacks an explicit statement of what happens for invalid/unknown codes, but the schema enforces the range and the use cases cover the primary agent scenarios. The absence of an output schema is mitigated by the description's explicit mention of the return value.

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?

The schema only defines 'code' as an integer 100-599 with no description. The description compensates by explaining the parameter as a 'numeric HTTP status code' with examples 404 and 429, adding meaning beyond the raw schema. It doesn't explicitly enumerate the full range, but the schema already handles that.

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 uses a specific verb 'Explain' and identifies the resource 'numeric HTTP status code'. It clearly states the tool returns the standard reason phrase and a short description, which distinguishes it from sibling lookup tools like mime_lookup.

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 provides explicit 'Use when' and 'Do not use when' sections, with concrete examples like 'What does HTTP status 404 mean?' and alternatives such as 'use mime_lookup'. This is exemplary usage guidance.

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