Autocomplete a Nigerian postcode

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

Annotations already declare readOnlyHint, idempotentHint and openWorldHint, so the safety profile is covered. The description adds genuinely useful non-structured context — that the call is free — plus the correct call sequence for the complete-code path. It does not describe result-set size or partial-match behavior for non-existent prefixes, but that is largely covered by the output schema.

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?

Three short sentences, zero filler, and the identifying purpose is front-loaded before the routing advice. Every sentence earns its place.

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 one fully documented parameter, annotations covering safety, and an output schema handling return values, nothing an agent needs in order to select or invoke this tool is missing. Sibling routing is included for the ambiguous complete-code case.

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 coverage is 100% and the schema itself supplies the example ('EK 01 A') and length bounds, so the description has little left to add. It conveys the 'partly typed / prefix' semantic through the usage sentence, which is a small value-add over the schema.

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?

States a specific verb (suggest/autocomplete), a specific resource (Nigerian postcode), and the exact scope (next segment of a partly typed code). It is immediately distinguishable from validate_postcode and lookup_postcode, which handle complete codes.

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?

Explicitly names the triggering condition (user still typing, or only the start of the code is known) and explicitly routes the complete-code case to validate_postcode then lookup_postcode. Both when-to-use and the alternative path are stated.

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