os_places_by_postcode

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

Annotations already mark this tool as readOnly, idempotent, and openWorld, so the safety profile is well covered. The description adds the backend ('OS Places API') and result kind, but does not disclose behaviors such as multiple UPRNs per postcode or postcode normalization. It is consistent with the annotations but does not meaningfully expand on them.

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 a single front-loaded sentence stating the action, input, and output with no filler. It is appropriately sized for a simple lookup tool and every word contributes to understanding.

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?

With readOnly, idempotent, and openWorld annotations plus an output schema, the description does not need to document return values or side effects. It is complete enough for a one-parameter lookup tool, though it could improve by specifying that a full UK postcode is expected and by pointing to alternative os_places tools for non-postcode inputs.

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 describes the only meaningful parameter as 'UK postcode', and the description largely repeats that phrase without adding accepted formats, partial-postcode behavior, or spacing rules. The `tool` parameter is a const and needs no semantic explanation. Overall, the parameter meaning is adequate but no richer than the schema itself.

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 clear verb ('Lookup') with a specific resource and result: UPRNs and addresses for a UK postcode via the OS Places API. The postcode-scoped purpose distinguishes this from sibling tools like os_places_by_uprn, os_places_nearest, and os_places_radius. No ambiguity remains about what operation is performed.

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 implies the use case: when an agent has a UK postcode and needs UPRNs or addresses. However, it does not explicitly state when not to use it or name alternatives such as os_places_search or os_places_nearest. The context is clear but the guidance stops short of helping an agent choose among the many os_places_* siblings.

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