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

Annotations already declare readOnly, idempotent, non-destructive and non-openWorld, so the safety profile is covered. The description adds genuinely new behavior: alias resolution (passport→passport-renewal-adult, brp→evisa, sorn→vehicle-tax-sorn) and the unknown-key response shape, which the annotations cannot convey.

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 and organized by concern, but the 16-service enumeration duplicates the schema enum and the change-list examples (passport fees from 8 April 2026, BRP → eVisa switch, etc.) are verbose detail that an agent rarely needs at selection time.

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 usefully describes the return payload (official page, startUrl, last update date, figures with value/unit/quoted sentence/source URL, dated change list). For a single-parameter read tool this is close to complete, though pagination/size limits are unaddressed.

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%, so the baseline is 3. The description largely restates the enum and the alias examples the schema already lists, though it does add the full alias mapping and the 'omit to list all' behavior — marginal value over structured data.

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 precise verb+resource ('Current UK government service facts verified against gov.uk, by service') and enumerates the exact service keys covered, so an agent knows exactly what domain this answers for. No siblings exist to confuse it with.

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?

Gives concrete routing behavior: omit the parameter to list all services, and an unknown service returns covered:false with the nearest keys. There is no sibling tool to contrast against, so full when/when-not guidance is not applicable, but the fallback semantics are made explicit.

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