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

Annotations already declare readOnlyHint=true, destructiveHint=false and openWorldHint=true, so safety is covered; the description adds real value by disclosing failure behavior (an 'not_found' error when CAC publishes no TIN). It does not mention rate limits or whether results can go stale, which keeps it below a 5.

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 purpose and immediately followed by the input contract and the return shape. The return-value sentence is somewhat redundant given an output schema exists, but it is brief and also carries the error case, so it still earns its place.

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 three-required-parameter read tool with a full output schema, the description covers purpose, parameter provenance, and the one non-obvious failure mode — everything an agent needs to call it correctly.

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 100% and each parameter already states it comes from search_cac_register, so the description's recap of those three field names adds little new meaning. The provenance framing is useful for chaining but duplicates the schema rather than extending 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 ("Get the Tax ID (TIN)") plus the source ("CAC's public search"), which separates it cleanly from siblings like search_cac_register and check_annual_returns. An agent can tell this is a follow-up lookup keyed on an existing search result.

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?

Implicitly and clearly positions the tool as a step after search_cac_register by naming the exact fields to carry over, which is strong contextual guidance. It stops short of stating when not to use it or what to do if the caller has no search result, so it is not a full when/when-not treatment.

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