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 this is a read operation ('Get'), implying it's non-destructive, but does not disclose behavioral traits such as authentication requirements, error handling (e.g., if href is invalid), rate limits, or what 'full details' includes. This leaves gaps in understanding how the tool behaves beyond its basic purpose.

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 appropriately sized and front-loaded: the first sentence states the purpose clearly, and the Args section efficiently explains the parameter. There is no wasted text, and every sentence adds value, making it easy for an agent to parse and understand quickly.

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 that there is an output schema (which likely defines the return structure), the description does not need to explain return values. However, with no annotations and only basic parameter info, it lacks details on authentication, error cases, or behavioral nuances. For a simple read tool, it's adequate but has clear gaps in completeness, especially around operational context.

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 description adds significant meaning beyond the input schema, which has 0% description coverage. It explains that 'href' is 'The href/URL path of the .ics resource' and specifies it should be 'as returned by calendar_list_events', clarifying the parameter's source and format. This compensates well for the lack of schema descriptions, though it doesn't detail syntax constraints like URL encoding.

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 ('Get full details') and resource ('a single CalDAV event'), distinguishing it from siblings like calendar_list_events (which lists events) and calendar_create_event (which creates events). It precisely defines the scope as retrieving details for one event identified by its href.

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 by specifying that the href should come 'as returned by calendar_list_events', giving a practical usage hint. However, it does not explicitly state when to use this tool versus alternatives like calendar_list_events for summaries or calendar_update_event for modifications, missing explicit exclusions or comparisons.

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