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

Beyond the readOnly/idempotent annotations, it discloses rate-limit accounting ('each postcode counts as one request'), the unknown-never-no data semantics, source attribution and dates per field, and a not-legal-advice disclaimer. These are exactly the behavioral traits an agent cannot infer from structured fields.

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 the usage trigger, then outputs, then caveats and limits. Dense but every sentence carries information; the run-on enumeration of comparison fields is long but functionally necessary given no output schema.

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, the description fully enumerates the returned fields and the comparison table columns, plus data-quality semantics and rate-limit cost. An agent has everything needed to call this correctly and to interpret the response.

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 both parameters are already documented, and the description only reinforces the 2-to-4 postcode bound. The household parameter and its enum implications are never discussed in the description, so it adds little beyond 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 (compare), resource (2-4 rented homes or areas in England), and scope (by postcode). It is clearly differentiated from siblings like check_address (single address) and area_market (single area) because it returns both plus a comparison table.

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 leading clause 'Use when someone wants to compare 2 to 4 rented homes or areas in England by postcode' gives a clear trigger condition and cardinality bound. It does not explicitly name alternatives like check_address or area_market for single-item lookups, so the routing guidance is implicit rather than exhaustive.

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