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

Annotations already declare readOnlyHint, idempotentHint, openWorldHint and destructiveHint=false, so the safety profile is covered. The description adds real value beyond that by disclosing the billing model ('free within the daily allowance, then $0.002 USDC per call via x402'), which an agent needs to reason about cost-sensitive repeated calls.

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 short sentences, scope first and pricing second, with no filler. Every clause carries information the agent cannot get from the structured fields.

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 no explanation, and annotations cover the safety profile. However, for a search tool the description leaves matching semantics (exact vs fuzzy, minimum query length) and disambiguation from autocomplete/lookup unstated, which is the practical gap.

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 both parameters ('Place name', 'Max results'), so the schema carries the load. The description adds only the implied scope of 'q' and says nothing about result ordering, defaults for limit, or matching behaviour, 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?

States a specific verb and resource and narrows the resource ('UK places (towns, villages, suburbs) by name'), which cleanly separates it from the postcode-oriented siblings (lookup, reverse, outcode, validate). An agent can tell what this returns without opening the 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?

The description never says when to pick this over uk-postcodes__autocomplete (partial input) or uk-postcodes__lookup (known postcode). It also doesn't state whether 'q' must be an exact/full place name or accepts partial matches, which is the main decision an agent faces here.

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