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

Annotations already cover read-only, idempotent, non-destructive, closed-world behavior, so the bar is lower. The description adds real value beyond them: it discloses that a match may not exist ('if any') and describes the two-step workflow into `fetch` for verdicts and reports, which annotations cannot express.

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?

Three short sentences, front-loaded with the resource and scope, then input format, then return and next step. No sentence is redundant with another or with structured fields.

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 single-parameter read tool with an output schema and full annotation coverage, this covers everything the agent needs: scope, accepted format, negative constraint, possibility of no match, and where to go next. Nothing essential 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%, so baseline is 3. The description goes beyond the schema by constraining the input negatively ('not a name or free text') and giving both international and national formats, which reduces wasted calls with names as queries.

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 ('Find a phone number in the Calmido directory') plus the geographic scope (NL/BE/LU), and the final sentence distinguishes it from `fetch` by explaining the handoff. It does not differentiate itself from the sibling `lookup_phone_number`, whose name suggests an overlapping purpose, leaving some ambiguity for the agent.

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?

Explicitly says what the query is and is not ('it is not a name or free text') and describes the follow-on step ('Pass its id to `fetch`'), which gives clear usage context. There is no explicit rule for choosing this over `lookup_phone_number`, so the alternative-selection guidance is incomplete.

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