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

Annotations already declare readOnlyHint=true, so safety is covered; the description adds genuinely new behavioral context — no API key required and free to call — which materially affects whether an agent tries it. It stops short of saying what the response contains or whether it makes a live network call, but for a zero-param status probe that gap is small.

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 plus a routing clause, with no filler; the free/no-key qualifier and the tool's purpose both land in the first clause. Every sentence carries a distinct job: what it does, then where else to go.

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 no-param, read-only status tool with no output schema, the description covers purpose, cost/auth, and intent routing, which is nearly everything an agent needs. A hint at what the response shape looks like (e.g. boolean availability vs version string) would close the last 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?

Zero parameters, so the baseline is 4 and there is nothing for the description to disambiguate. The absence of any parameter discussion is appropriate rather than an omission.

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 three named facets of the check (UK Source Intelligence availability, free-trial readiness, API version), which no sibling tool covers. The 'FREE, NO KEY' prefix front-loads the distinguishing constraint. An agent can tell this apart from start_free_trial or get_govuk_change_brief 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?

Explicitly routes two alternative intents away: historical change questions go to get_govuk_change_brief, live source quotes go to preview_source_evidence. The remaining intent (checking service/trial/version status) is the only one left, so the selection is unambiguous.

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