mask_email

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

No annotations are provided, so the description carries the burden. It discloses default behavior: 'By default shows the first 2 characters of the username and keeps the domain visible.' This adds context not available in the schema, such as the exact masking behavior. It could be richer by describing output format or edge cases, but for a simple pure function it is adequate.

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 two sentences long, the first stating the core purpose and the second conveying usage context and default behavior. Every word serves a purpose, with no redundancy or unrelated information. It is front-loaded with the action.

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?

Given that the tool is a simple string transformation with no output schema and no annotations, the description adequately covers purpose, usage, and defaults. It does not explicitly describe the return value or behavior for invalid input, but these are not critical for a straightforward masking function. The overall definition is sufficiently complete for an agent to invoke 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%, so all four parameters are documented with defaults and examples. The description's statement about default behavior (first 2 characters, domain visible) essentially re-states the schema defaults for visibleChars and maskDomain, adding no new parameter-level meaning. Hence, baseline is 3 with no additional value.

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 begins with a specific verb and resource: 'Masks an email address to protect user privacy.' This clearly distinguishes it from the sibling tool mask_card by specifying the resource type (email address) and the action (masking).

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?

The description provides clear usage context: 'Use when the user wants to hide, anonymize, or partially obscure email addresses in a table, UI, or logs.' This tells the agent when to apply the tool, though it does not explicitly mention alternatives or exclusions. The sibling mask_card inferentially covers cards, so the usage boundary is clear.

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