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

Annotations already declare readOnly, idempotent, openWorld, and non-destructive, so the safety profile is covered. The description adds pricing behavior (free within daily allowance, then $0.002 USDC via x402), which is genuinely useful context beyond the annotations. Output schema exists, so return format need not be described.

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?

Two short sentences, front-loaded with the purpose followed by pricing. No wasted words.

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 description covers the core purpose and pricing, and annotations plus schema plus output schema handle much of the burden. However, it lacks any usage guidance or sibling differentiation, which for a tool in a large family of 'near'/'nearest' tools leaves a notable gap.

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 (postcode, limit) are already documented in the schema. The description adds no parameter-level detail beyond what is provided.

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 verb (find) and resource (postcodes nearest to a given UK postcode), making the purpose immediately clear. It doesn't explicitly distinguish itself from siblings like uk-postcodes__reverse, though the 'nearest' semantics are reasonably self-evident.

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?

There is no guidance on when to use this tool versus alternatives like uk-postcodes__reverse or uk-postcodes__places. The only context given is pricing, not usage conditions.

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