pyfastmail-mcp

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

No annotations are provided, so the description carries full burden. It mentions authentication ('authenticated Fastmail account'), which is useful. However, it lacks details on behavioral traits like pagination, rate limits, error handling, or what data is returned (though output schema exists). More context on typical use cases or constraints would improve transparency.

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 a single, efficient sentence with no wasted words. It is front-loaded with the core action and resource, making it easy to understand quickly. Every part of the sentence contributes essential 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 0 parameters, 100% schema coverage, and an output schema exists, the description is reasonably complete. It specifies the resource (CalDAV calendars) and authentication context. However, for a list operation with no annotations, adding brief notes on output format or common use cases could enhance completeness, though not strictly necessary.

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?

There are 0 parameters, and schema description coverage is 100%, so the baseline is high. The description adds no parameter-specific information, which is fine since no parameters exist. It effectively communicates the tool's purpose without needing to detail inputs.

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 verb ('List') and resource ('all CalDAV calendars'), specifying the scope ('for the authenticated Fastmail account'). It distinguishes from siblings like calendar_list_events (which lists events within calendars) by focusing on calendars themselves.

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 when needing to enumerate calendars, but does not explicitly state when to use this tool versus alternatives (e.g., calendar_list_events for events, or other list tools). No exclusions or prerequisites are mentioned, leaving some ambiguity.

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