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

Annotations already declare readOnlyHint, openWorldHint and idempotentHint=false, so the safety profile is covered. The description adds genuinely new context: data provenance (official ONS and police data under OGL), the recency window (latest published month, ~1 mile radius), and the cost/auth mechanics ($0.01 USDC per call via x402 or prepaid credits, free trial). It omits rate limits or failure modes but is well above the annotation-only baseline.

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 sentences, each doing work: first the payload, then provenance, then pricing. The main capability is front-loaded. The pricing sentence is slightly administrative but is legitimately decision-relevant for an agent choosing a paid tool.

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 structure need not be explained, and the description still conveys what categories of data come back, their currency, and their geographic scope. Combined with 100% schema coverage and safe-read annotations, an agent has enough to call this correctly; only explicit alternative-routing 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 description coverage is 100% and both parameters (outcode, postcode) are documented with examples and max lengths in the schema itself. The description mentions 'postcode or postcode district' and the SW1A example, consistent with the schema but adding no syntax or format detail beyond it. Baseline 3 is appropriate.

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 the resource (UK area profile) and the key input (postcode or postcode district, e.g. SW1A), then enumerates the payload: local authorities, wards, constituencies, and street-level crime by category and outcome. That is far more specific than a tautology and lets an agent distinguish it from siblings such as uk-postcode or uk-food-hygiene by content. It stops short of explicitly naming a sibling it is not, so a 4 rather than a 5.

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 is implied by the input framing ('for a postcode or postcode district') and by the fact that the free trial and pricing are stated, but there is no explicit when-to-use, when-not-to-use, or named alternative (e.g. uk-postcode for a plain lookup). The agent can infer the context but must reason about it.

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