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

Annotations already declare readOnly/idempotent/non-destructive, and the description adds real context on top: a 30-per-minute rate limit, that the operation is free, and a meaningful authorization nuance ('The key that ran the check also sees its reference; anyone else, the public view'). That access-scoping detail is behavioral information an agent cannot derive from the schema or annotations.

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?

Dense but organized with Inputs/Returns/Limits labels, so an agent can scan to the part it needs. It leads with the return payload rather than the purpose action, and a few clauses restate schema content, which slightly dilutes front-loading.

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 two-parameter read tool with annotations and an output schema, the description is fully sufficient: it explains what is returned, how to render it ('show it as is'), the rate limit, and the access model. Nothing needed to call it correctly is missing.

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% and the enum already documents the two formats, so the baseline is 3. The description adds a concrete proof-code example, confirms case-insensitivity, and clarifies that a lookup's meta.receipt.request_id is 'the same key' — the equivalence claim is genuinely useful even though the schema hints at it.

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 ('give back the Fuentio receipt of a verification by its proof code') and immediately enumerates the payload, so the agent knows exactly what comes back. It explicitly distinguishes itself from the sibling 'verify_company', which is the closest confusable tool.

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?

Gives when to use ('when the user asks for a receipt or proof of a check'), when NOT to use ('Don't use it to run a new check: call verify_company'), and even the required interaction step ('Always ask the user first: Normal or detailed receipt?'). The alternative is named explicitly, leaving nothing to inference.

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