pyfastmail-mcp

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

No annotations are provided, so the description carries full burden. While 'Create' implies a write/mutation operation, it doesn't disclose behavioral traits like authentication requirements, rate limits, whether the address is immediately usable, what happens on duplicate requests, or the typical response format. The description lacks essential context for a creation tool.

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 well-structured with a clear purpose statement followed by parameter explanations. Every sentence adds value, though the parameter section could be slightly more concise by integrating format constraints directly rather than as parenthetical notes.

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 no annotations, 0% schema description coverage, but presence of an output schema, the description is moderately complete. It covers the core purpose and parameters well, but lacks behavioral context (permissions, side effects) that would be important for a creation tool. The output schema will handle return values, reducing the burden.

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 0%, so the description must compensate. It provides clear semantic explanations for all three parameters: 'for_domain' specifies the domain context, 'description' explains it's user-supplied context, and 'email_prefix' clarifies it's optional with character restrictions. This adds substantial value beyond the bare schema.

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 clearly states the specific action ('Create a new masked email address') and distinguishes it from sibling tools like 'mail_list_masked_emails' or 'mail_update_masked_email_state'. It specifies the resource being created (masked email address) with no ambiguity.

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 no guidance on when to use this tool versus alternatives. It doesn't mention prerequisites, when not to use it, or differentiate from similar tools like 'mail_create_mailbox' or 'mail_list_identities'. The agent must infer usage from the name alone.

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