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 non-obvious failure mode: it refuses with a do_not_answer sentinel rather than guessing when content is drifted or unverified. It omits other behavioral facts an agent needs — what happens for an unknown or malformed fact_id, and whether the refusal is an error or a normal payload.

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, front-loaded with the core action, with no filler. The clause 'never guesses' slightly restates the preceding refusal statement, costing a little density.

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 one-parameter read tool with no output schema, the description is minimal but not misleading. However, with no output schema the description should sketch the return shape (fact text, verification status, the do_not_answer sentinel) and where fact_ids come from; those gaps matter because nothing else documents them.

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?

The single parameter has 0% schema description coverage, so the description must compensate and does not: it says nothing about the expected format of fact_id or where to source a valid id. The only meaning added is that the id refers to a 'verified fact' in the mileageuk pack, which is minimal.

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 concrete verb and resource ('Get one verified fact') scoped to the mileageuk pack, so it is distinguishable from the sibling mileageuk_list_facts and mileageuk_changes by scope. It does not explicitly name those siblings, so the differentiation is inferred rather than stated.

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 only implied: 'Get one verified fact' suggests retrieval by a known fact_id, but the description never says to obtain ids from mileageuk_list_facts first or when to prefer mileageuk_changes / mileageuk_list_facts instead. No when-not conditions beyond the refusal case.

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