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

With no annotations, the description carries the full burden, and it does disclose a valuable non-obvious trait: it refuses with a do_not_answer signal when the fact has drifted or is unverified, and never guesses. That is real behavioral signal, but it doesn't define "drifted," describe the response shape, or indicate any auth or rate considerations.

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 with no filler; the core action leads and the refusal constraint follows. Each sentence carries information, though the parenthetical do_not_answer token could be integrated more cleanly.

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 single-parameter read tool with no output schema, the definition covers the action and the key failure mode, which is the minimum an agent needs. It leaves open how to acquire a fact_id and what a successful response contains, both of which matter for correct invocation in this large pack of similar tools.

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 0% for the single required fact_id parameter, so the description must compensate — but it says nothing about the identifier's format or where an agent obtains one (presumably from taxfreeuk_list_facts). The only implicit aid is the phrase "one verified fact," which hints fact_id addresses a single record.

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 ("Get one verified fact") scoped to the taxfreeuk pack, and the singular "one verified fact" implicitly contrasts with the sibling taxfreeuk_list_facts. It stops short of naming that sibling or clarifying the relationship to taxfreeuk_changes.

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 singular framing implies retrieval of a specific known fact rather than browsing, but the description never states when to pick this over taxfreeuk_list_facts or taxfreeuk_changes. An agent must infer the workflow (list, then get by id) rather than being told it.

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