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

Annotations already declare readOnly, idempotent, openWorld and non-destructive, so the safety profile is covered. The description adds genuinely useful behavioral context beyond that: a free-sample quota per day and a $0.002 USDC charge per call via x402, which an agent must know before invoking. It does not state error behavior for invalid postcodes, keeping it short of 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?

Two sentences, zero filler. The resource list is front-loaded and the cost/quota constraint follows immediately, so the most decision-relevant facts come first.

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?

An output schema exists, so return values need not be re-specified; annotations cover safety. The description fills the one gap the structured data cannot (per-call pricing and quota). It is nearly complete for a single-parameter lookup, missing only postcode-format tolerance and invalid-input behavior.

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?

With a single parameter at 100% schema description coverage, the schema already documents 'postcode' as a UK postcode string. The description adds no format, casing, or validation detail beyond that, so the baseline 3 applies.

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 names a concrete verb-resource pair (administrative lookup for a postcode) and enumerates the exact outputs: council with website and tier, ward, parish, constituency, police force, NHS ICB. It is clear what you get back, though it never explicitly distinguishes itself from the uk-geography__local-authority / ward / parish / constituency siblings that cover the same concepts individually.

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?

There is no guidance on when to use this aggregate tool versus uk-geography__local-authority, uk-geography__ward, or uk-postcodes__lookup/validate. The only operational context given is the pricing model, which tells the agent about cost but not about selection criteria or prerequisites.

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