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

The description adds useful behavior beyond the readOnly/openWorld annotations: it warns about upstream rate limiting and explains that incomplete postcodes yield suggestions. This helps the agent anticipate throttling and non-exact results, though it does not detail error behavior or suggestion format.

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 convey the core behavior, a caveat, and the edge-case behavior without any filler. The most important information is front-loaded: what the tool returns, then the rate-limit warning.

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 read-only lookup, the description is largely complete: it names the input domain, the output type, and a special case. It could have described the exact shape of returned addresses or suggestions, but the absence of an output schema is partially mitigated by the straightforward nature of the tool.

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 postcode parameter already has a clear example ('NW2 7JW'). The description itself adds no further parameter-level detail, so the baseline of 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 clearly states the resource and action: it returns addresses for a UK postcode. It also clarifies the incomplete-postcode case where suggestions are returned. There are no sibling tools overlapping with postcode lookup, so no ambiguity remains.

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 intended use is obvious from the description: call it when an address lookup for a UK postcode is needed. It also covers the partial-postcode case by noting suggestions, providing clear context. It does not explicitly state when not to use it, but no alternative address tool exists among the siblings.

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