Validate a PAN

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

Annotations already declare readOnlyHint, idempotentHint and openWorldHint=false, so safety is covered. The description adds behavior beyond that: the check is performed offline and a pass has bounded meaning (no issuance, no ownership attestation), which prevents over-trusting the result. What's missing is the shape of the return value (boolean vs. structured result), so it falls short of 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?

Two sentences, no filler. The positive capability is stated first and the limitation ('a pass does not prove...') is front-loaded as a caveat in the second sentence. Every clause carries information.

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-only, no-output-schema validator this is nearly sufficient: the rules checked and the limits of a pass are both covered. The only gap is that it doesn't indicate the response shape — e.g., whether it returns only a boolean or also the decoded holder type — which matters since no output schema exists.

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 there is only one parameter, so baseline is 3. The description earns above baseline by adding real meaning to the input: the exact 10-character structure and the fact that character 4 encodes holder type, which the schema's 'The 10-character PAN' does not convey.

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?

The description gives a specific verb and resource: 'Checks an Indian PAN offline', and then enumerates exactly which rules are checked — the 5-letter/4-digit/1-letter shape and the holder-type character in position 4. This is enough to tell it apart from siblings like validate_gstin or validate_aadhaar_format without opening any schema.

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?

Usage context is clear: it is an offline format validator, not an issuance or ownership check, and the description states that a pass does not prove the PAN was issued or who owns it. It doesn't explicitly contrast with a hypothetical online lookup or name alternatives, but with a sibling set of distinct per-identifier validators the selection is unambiguous.

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