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

Annotations already cover readOnly/idempotent/openWorld/non-destructive, but the description adds real behavioral context: Delivery Area localities only, postcode/name ordering, multiple localities per postcode, and that the public endpoint returns English natural-language text with pagination preserved. The phrase 'preserving sources, conditions and pagination' is vague enough to leave some ambiguity.

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?

Front-loaded with purpose and searchable keys, then routing, then return characteristics. All sentences earn their place, though the closing clause about 'sources, conditions and pagination' is compressed to the point of being cryptic.

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 no output schema and 4 parameters, the description supplies what matters most: what is returned (Delivery Area localities, ordering, multiple per postcode), pagination existence, locale effects, and sibling routing. It does not describe page/pageSize limits or empty-result behavior, leaving a small 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 coverage is 50%: query and locale are documented in-schema, while page and pageSize have no descriptions in either place. The description reinforces query (postcode/locality name) and implies paging behavior, but adds little that the schema does not already say, so baseline 3 is appropriate.

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 (Search) and resource (website postcode directory) plus the searchable keys (postcode, English/Chinese locality name). It explicitly distinguishes itself from two near neighbors: get_postcode and the course-campus postcode filter, so the agent can select it without opening the schema.

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?

Gives clear routing: use get_postcode for regional classification and associated schools, and explicitly notes this is not the course-campus postcode filter. No explicit statement of when-not to use this tool beyond that negative, so it falls short of a full alternative map.

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