pyfastmail-mcp

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

No annotations are provided, so the description carries the full burden. It discloses that the file is returned as base64 (a key behavioral trait), but does not mention authentication requirements, rate limits, error conditions, or whether the operation is read-only (implied by 'download' but not explicit). It adds some value but leaves gaps for a tool with no annotation coverage.

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 front-loaded with the core purpose in the first sentence, followed by a concise parameter explanation. Every sentence earns its place with no wasted words, and the structure is clear and efficient.

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 the tool has an output schema (which handles return values), no annotations, and a simple single parameter, the description is mostly complete. It covers the purpose, parameter semantics, and key behavioral detail (base64 return). However, for a tool with no annotations, it could better address authentication, errors, or operational constraints to be fully comprehensive.

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?

The schema description coverage is 0%, so the description must compensate. It provides a clear example for the single parameter ('path: Path to the file (e.g., "/Documents/report.pdf")'), adding meaningful semantics beyond the schema's basic string type. This adequately covers the parameter, though it could note path format constraints or validation rules.

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 ('Download a file') and resource ('from Fastmail Files (WebDAV)'), and it distinguishes from sibling tools like files_list (list files), files_upload (upload), and files_delete (delete). The mention of base64 return format adds precision beyond just 'get'.

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 downloading files, but does not explicitly state when to use this vs. alternatives like files_list (to browse) or mail_download_attachment (for email attachments). It provides clear context for file retrieval from Fastmail Files, but lacks explicit exclusions or comparisons to sibling tools.

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