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 states the tool uploads a blob but lacks details on permissions, rate limits, error handling, or what happens after upload (e.g., blob storage, expiration). This leaves significant behavioral gaps for a mutation 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 front-loaded with the main purpose, followed by parameter explanations in a clear 'Args:' section. It is appropriately sized with no redundant information, though it could be slightly more concise by integrating parameter details into the opening sentence.

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 coverage, and an output schema (which reduces need to explain returns), the description is moderately complete. It covers the basic purpose and parameters but lacks behavioral context (e.g., auth needs, side effects) and usage guidelines, leaving gaps for a mutation tool.

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%, but the description compensates by explaining each parameter's purpose: 'data' as base64-encoded content, 'content_type' as MIME type, and 'name' as informational filename. This adds meaningful semantics beyond the bare schema, though it could detail constraints like max file size.

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 tool's purpose: 'Upload a blob for use in email composition.' It specifies the verb ('upload') and resource ('blob'), but does not distinguish it from sibling tools like 'files_upload' or 'mail_download_attachment', which reduces clarity in context.

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?

No explicit guidance on when to use this tool versus alternatives is provided. The description mentions 'for use in email composition,' which implies a context but does not specify prerequisites, when not to use it, or direct alternatives among sibling tools.

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