pyfastmail-mcp

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

With no annotations provided, the description carries full burden. It discloses key behaviors like threading preservation, quoting, and auto-selection of identity, but doesn't mention permission requirements, rate limits, error conditions, or what the output contains. For a mutation tool with zero annotation coverage, this leaves significant gaps.

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?

Perfectly structured with a clear purpose statement followed by parameter explanations. Every sentence adds value with zero waste. The Args section is well-organized and directly supports tool invocation.

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 mutation tool with 4 parameters, 0% schema coverage, and no annotations, the description does well on parameters but lacks behavioral context about permissions, side effects, and error handling. The presence of an output schema reduces the need to describe return values, but more operational guidance would be helpful.

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 meaningful explanations for all 4 parameters beyond their titles: email_id identifies the target, text_body is the reply content, reply_all controls CC behavior, and identity_id has auto-selection logic. This adds substantial value over 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 ('Reply to an email'), the resource ('an email'), and key behavioral details ('preserving threading headers and quoting the original'). It distinguishes itself from sibling tools like mail_send_email by focusing on replying within an existing thread.

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 context by specifying it's for replying to an existing email, but doesn't explicitly state when to use alternatives like mail_forward_email or mail_send_email. It provides clear parameter guidance (e.g., identity_id auto-selects if omitted) which helps with practical usage.

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