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

Annotations already cover read-only, open-world, idempotent and non-destructive traits, so the bar is lower. The description adds real context beyond them: it is a compatibility shim forced by search/fetch-style clients, it targets a specific external site, and its output feeds the fetch sibling. It does not mention rate limits or pagination, but the output schema covers returns.

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?

Compact — two sentences that each carry load. The client-compatibility caveat comes first rather than the core action, so it is not perfectly front-loaded, but there is no filler and no redundancy.

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 one-parameter read tool with full annotations and an output schema, the description supplies everything an agent needs: the compatibility rationale, the preferred alternative, the target source, and how results connect to fetch. Nothing material is missing.

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% for the single parameter, and the schema already documents that the string is free text containing a UK postcode with examples. The description repeats "a UK postcode contained in the query" without adding parsing rules or format constraints, so the 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?

State a specific verb and resource: "Searches fibrecompare.com for broadband deals available at a UK postcode." It also distinguishes itself from both siblings by naming check_fibre_availability as preferred and explaining that results are "deal ids for fetch," so an agent can place it in the workflow without opening any 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?

Explicitly scopes when to use it ("Compatibility tool for clients that require search/fetch, e.g. ChatGPT deep research") and when not to ("Prefer check_fibre_availability"). Both the routing condition and the exclusion are stated, leaving nothing to inference.

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