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

Annotations already declare readOnly/idempotent/non-destructive/closed-world, so the bar is lower; the description adds real behavioral context by disclosing the compact-by-default response shape (claim start, label, receipt link) and what the full mode surfaces. It stops short of describing match ranking or result-count behavior beyond the schema's max_results.

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 tight sentences with zero filler; the default behavior is front-loaded and the mode toggle follows immediately. Nothing repeats the schema verbatim.

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?

With no output schema, the description usefully characterizes both return modes, which is the main gap it needed to fill. It is slightly incomplete on sibling routing (when this beats check_claim) and on what a 'receipt link' actually points to.

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 100%, so baseline is 3; the description earns a bump by explaining the practical consequence of the detail flag — compact versus full wording — which is more actionable than the schema's 'Full claim, what checked it and what is not proven'. It says nothing extra about query or max_results.

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?

Specific verb+resource: "Search the library of machine-checked facts" tells the agent exactly what corpus is being queried, which the name alone ('lookup_fact') does not. It does not, however, differentiate itself from siblings check_claim or search_attempts, so an agent must infer the boundary.

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 second sentence implies usage via the detail toggle (compact for scanning, detail for full wording), but there is no explicit statement of when to choose lookup_fact over check_claim or search_attempts, and no exclusions or prerequisites.

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