pyfastmail-mcp

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

With no annotations provided, the description carries the full burden. It effectively discloses that this is a mutation tool (sending emails), mentions the API integration (JMAP), and provides important security warnings about html_body injection risks. However, it doesn't cover rate limits, authentication requirements, or error behaviors.

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?

Well-structured with a clear opening statement followed by parameter documentation. The security warning for html_body is appropriately placed and necessary. Could be slightly more front-loaded but overall efficient with minimal waste.

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 7-parameter mutation tool with no annotations, the description provides substantial parameter documentation and important behavioral context. The presence of an output schema reduces the need to describe return values. It covers the essential sending functionality well but could benefit from more usage guidance relative to sibling tools.

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?

With 0% schema description coverage, the description fully compensates by explaining all 7 parameters in detail. It clarifies optional vs. required parameters, provides security warnings for html_body, explains default behavior for identity_id, and adds meaningful context beyond basic parameter names.

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 ('Send an email') and the resource ('via Fastmail'), distinguishing it from sibling tools like mail_reply_to_email or mail_forward_email. It's precise about the core functionality without being tautological.

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 implies usage for sending emails but doesn't explicitly state when to use this versus alternatives like mail_reply_to_email or mail_forward_email. It provides some contextual guidance about html_body security but lacks explicit when/when-not directives or sibling tool comparisons.

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