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 genuinely useful behavioral context the annotations lack: the pricing model (free within daily allowance, then $0.002 USDC per call via x402). It does not, however, mention auth requirements or rate-limit specifics beyond cost.

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, with the core purpose front-loaded and cost information appended. Every sentence carries weight, though the pricing sentence is somewhat tangential to selection.

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 single-parameter tool with an output schema (so return values need not be explained) and annotations covering safety, the description is nearly complete. The main gap is the absence of routing guidance relative to sibling postcode tools.

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% and the single parameter is documented as 'Retired postcode'. The description adds no syntax or format detail beyond what the schema already conveys, 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 states a specific resource and scope: termination date and location for a retired UK postcode. It implicitly distinguishes itself from active-postcode siblings like lookup/validate, though it never names them explicitly. The phrasing 'When a retired UK postcode was terminated, and where it was' is clear enough for selection.

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 explicit when-to-use guidance and no named alternative. The word 'retired' implies the tool is for inactive postcodes, but the description never tells the agent to prefer uk-postcodes__lookup for live postcodes or validate for checking existence. Usage must be inferred.

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