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 discloses the chronological ordering behavior and that it returns all emails in the thread, which is valuable. However, it doesn't mention authentication requirements, rate limits, error conditions, or what happens with deleted/archived emails in threads. The description doesn't contradict any annotations (none exist).

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 front-loaded with the core functionality in the first sentence, followed by a brief but clear parameter explanation. Every sentence earns its place with no wasted words or redundant information.

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 (so return values are documented elsewhere), no annotations, and only one parameter with good semantic explanation in the description, this is reasonably complete. The main gap is lack of behavioral context about authentication, errors, or edge cases, but the presence of an output schema reduces the need for return value explanation.

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 schema has no descriptions for the email_id parameter), the description compensates by explaining that email_id is 'ID of any email in the thread.' This clarifies that you don't need the first email's ID, just any email in the thread. For a single parameter tool, this provides good semantic context beyond 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 ('Return all emails') and resource ('in the same thread as the given email'), with additional detail about ordering ('in chronological order'). It distinguishes from sibling tools like 'mail_get_email' (single email) and 'mail_search_emails' (search-based).

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 provides clear context about when to use this tool (to get all emails in a thread), but doesn't explicitly mention when not to use it or name specific alternatives. The sibling tool list shows related tools like 'mail_get_email' and 'mail_search_emails', but no explicit comparison is made in the description.

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