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

With no annotations supplied, the description carries the full burden and does disclose the non-obvious behavior: it refuses with a 'do_not_answer' sentinel when content has drifted or is unverified rather than emitting a plausible guess. That is genuinely useful for an agent's decision logic; the gap is that it doesn't say what a successful response looks like or what happens for an unknown fact_id.

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 and immediately followed by the failure mode. '— never guesses' is mildly redundant with the preceding refusal clause, but costs little.

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 simple one-parameter lookup the description covers the essential contract (what it returns conceptually and that it will refuse rather than fabricate). Since there is no output schema, it should at minimum sketch the success response shape and state that fact_id comes from legaluk_list_facts, which it omits.

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?

There is one required parameter with 0% schema description coverage, so the schema adds nothing. The description only implies that fact_id names 'one verified fact' in the legaluk pack; it gives no format, no source for obtaining IDs, and no constraint on valid values.

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 a named pack ('legaluk'), which implicitly separates it from the sibling legaluk_list_facts (many) and legaluk_changes (change log). It never names those siblings, so the differentiation is inferable rather than explicit.

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 single-fact scope implies you call this when you already have a fact identifier and want the authoritative value, but the description never says how to obtain a fact_id (e.g. via legaluk_list_facts) or when to prefer legaluk_changes instead. Usage is only implied.

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