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

Annotations already cover read-only, idempotent, non-destructive and closed-world behavior, so the bar is lower. The description still adds real context: the dataset is England-only, results carry an address_id intended for run_free_check, and long lists are expected. No pagination or result-count detail is given, which keeps it below a 5.

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, with the scope/return-value fact and the routing condition front-loaded. Every sentence carries either scope, output linkage, or usage guidance.

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 two-parameter lookup with no output schema, the description supplies everything needed: what is returned (address_id), the geographic scope, the narrowing option, and the trigger condition. Nothing an agent needs in order to call it correctly 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%, so postcode and house_number_or_name are already documented in the schema, establishing a baseline of 3. The description goes beyond the schema by explaining the purpose of the optional parameter ('to narrow a long list'), which the schema's type/form note does not convey.

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 (Lists) and resource (the homes at a postcode), bounds the geography to England, and names the downstream artifact (address_id for run_free_check). This separates it cleanly from check_rental_postcode and run_free_check 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?

"Use it when the renter has given a postcode but not which home" gives an explicit trigger condition, and it says when to add the optional parameter (to narrow a long list). It does not explicitly name check_rental_postcode as the alternative for an unknown/invalid postcode, so the routing is implied rather than exhaustive.

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