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

With no annotations, the description carries full responsibility for behavior disclosure. It only restates the operation name and gives no information about masking style (e.g., partial masking, asterisks), whether input is validated, or what the output looks like.

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 very short and front-loads the core action. However, the leading 'Mask:' prefix is redundant with the tool name and slightly wastes space, so it is not a perfect 5.

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?

The tool is simple, but with no annotations and no output schema, the description should explain return value and masking behavior. It does neither, leaving the agent to guess what the tool returns and how the masking is applied.

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 the email parameter is documented as 'Email to process', so the schema handles the parameter meaning. The description adds no parameter semantics beyond the schema, and its mention of cards and keys could lead an agent to expect parameters that do not exist.

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 clear action ('Mask sensitive data') and lists examples (emails, cards, keys), but the only input schema parameter is email, so the cards/keys examples are misleading. It also does not differentiate this generic tool from sibling tools like x402-mask-email, x402-mask-card, or x402-mask-phone.

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?

No guidance is given about when to use this tool versus the more specific mask tools or alternatives like redact or obfuscate-email. With dozens of sibling tools, an agent has no basis for choosing x402-mask over x402-mask-email.

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