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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so the safety profile needs no restating. The description adds genuinely useful context beyond them: response content is auth-dependent, with roughly a dozen datasets marked 'locked' for non-pass holders. It stops short of saying how locked fields are represented or what happens for an invalid or non-England postcode.

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?

It is a single sprawling sentence built from semicolon-separated catalogue lists, so the reader has to parse a data inventory before reaching the operationally important auth-gating clause. Because there is no output schema, enumerating return families earns some of its length, but the ordering buries the most decision-relevant fact near the end.

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 single-parameter read tool with no output schema, the description is substantially complete: it covers coverage area, granularity, the full data inventory, and the auth-dependent subset. The remaining gap is edge-case behavior on rejected postcodes and the representation of locked values, both of which an agent would need to interpret a 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?

Only one parameter exists and schema coverage is 100%, so the schema already carries maxLength and the 'Full England postcode, e.g. SE22 8DL' example. The description's 'one full England postcode' reinforces the fullness and country constraint but adds no format or validation detail the schema lacks, which is the baseline 3 case.

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?

The description states a specific verb and resource: area facts for 'one full England postcode', with a concrete enumeration of the fact families returned. It is clearly distinguishable in scope from school-oriented siblings, though it never names search_near_postcode as the nearby-area alternative, so differentiation is achieved by implication only.

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?

Usage constraints are embedded rather than stated as guidance: 'one full England postcode' implies no partial outcodes and no Scotland/Wales/NI coverage, and the pass/locked sentence implies results degrade for anonymous callers. There is no explicit when-to-use versus when-not-to-use statement and no reference to any sibling tool.

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