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

With no annotations, the description carries the full burden, and it discloses a genuinely unusual behavioral trait: the tool refuses with do_not_answer when a fact is drifted or unverified and never guesses. That failure-mode disclosure is valuable, but it omits what the refusal payload looks like and whether a partial or fallback path exists.

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, zero filler, with the capability stated first and the refusal behavior second. Nothing repeats the tool name or title and every clause carries information.

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 tool with no annotations and no output schema, the description covers the refusal case but says nothing about the shape of a returned fact, its provenance or freshness, or how an agent should recover from do_not_answer. Adequate but with clear gaps.

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 0% for the single fact_id parameter, so the schema adds nothing about format or provenance. The description implies the ID selects one fact but never says where IDs come from (presumably rentinguk_list_facts) or what a valid ID looks like.

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") plus the scope ("from the rentinguk pack"), which implicitly separates it from the list_facts and changes siblings that share the same prefix. It does not name a sibling explicitly, 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?

"Get one" implies single-item retrieval by identifier, which weakly signals that bulk discovery belongs to rentinguk_list_facts, and the refusal clause hints at a verification gate. There is no explicit when-to-use, when-not-to-use, or guidance on what to do after a do_not_answer result.

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