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

Beyond the annotations, it discloses pricing ($0.005 USDC via x402 on Solana), transport constraints (POST body only), output privacy behavior (credit card number masked), and an equivalent HTTPS endpoint. These are material behavioral facts an agent would not get from the annotations alone.

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?

The description is front-loaded with the core purpose and covered formats, then moves to transport, pricing, and endpoint details. It is dense but nearly all content earns its place; minor tightening could improve readability without losing 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?

There is no output schema and the description only hints at output behavior ('number masked in output') without explaining the response shape, validity fields, or error format. For a validator, an agent would benefit from knowing what a result object looks like, so this remains a gap despite strong input-side coverage.

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 the baseline is 3, but the description adds meaningful semantic structure: it clarifies that 'type'+'value' are single-item mode and 'items' is batch mode, which the schema does not express via oneOf or explicit mutual exclusivity. It also reiterates the 100-item cap and POST-body-only requirement.

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 states a specific verb and resource ('Offline format validator') and enumerates exactly which formats are covered, including batch scope ('up to 100 values'). It is clearly distinguishable from single-purpose siblings such as email_validate or iban_validate.

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?

It clearly explains the two supported usage modes (single {'type','value'} or batch {'items':[...]}) and enforces 'POST JSON body only (never in the URL)'. It lacks explicit guidance on when to choose this over narrower sibling validators, but the context is otherwise clear.

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