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 the destructive nature ('Delete') and a key behavioral constraint about system mailboxes, but doesn't mention permission requirements, whether deletion is permanent/reversible, rate limits, or what happens to emails in the mailbox. This provides basic but incomplete behavioral context.

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 perfectly concise with two sentences that each earn their place: the first states the core action, the second provides critical constraint information. No wasted words, well-structured, and front-loaded with the primary purpose.

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 this is a destructive operation with no annotations but with an output schema (which handles return values), the description covers the essential purpose and a critical constraint. However, for a deletion tool, it should ideally mention permission requirements or whether the action is reversible to be fully complete.

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 for the single parameter (mailbox_id), the description adds minimal value beyond what's implied by the tool name. It doesn't explain what format the ID should be, where to find it, or provide examples. The baseline is 3 since schema coverage is low but parameter count is minimal.

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 ('Delete') and target resource ('a mailbox by its ID'), distinguishing it from sibling tools like mail_rename_mailbox or mail_list_mailboxes. It provides precise scope information about what cannot be deleted (system mailboxes).

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 explicitly states when NOT to use this tool ('System mailboxes... cannot be deleted'), providing clear exclusion criteria. However, it doesn't mention when to use alternatives like mail_rename_mailbox or prerequisites for deletion, keeping it from a perfect score.

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