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, but doesn't disclose behavioral traits like whether this is a read-only operation, potential rate limits, pagination behavior, or what happens if no address books exist. The description is minimal and lacks important operational context.

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 zero waste. It's front-loaded with the core purpose and includes all necessary context without unnecessary elaboration. Every word earns its place.

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's simplicity (0 parameters, output schema exists), the description is reasonably complete. It specifies the resource type and authentication scope. However, as a list operation with no annotations, it could benefit from mentioning behavioral aspects like read-only nature or output format, though the output schema may cover return values.

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 tool has 0 parameters with 100% schema description coverage. The description doesn't need to explain parameters, and it correctly doesn't mention any. It adds value by specifying the resource type (CardDAV address books) and authentication context beyond what the empty schema provides.

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 action ('List all') and resource ('CardDAV address books') with specific scope ('for the authenticated Fastmail account'). It distinguishes from siblings like contacts_list (which lists contacts, not address books) and calendar_list_calendars (which lists calendars, not address books).

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 address books for Fastmail, but doesn't explicitly state when to use this vs. alternatives like contacts_list or calendar_list_calendars. No guidance on prerequisites (e.g., authentication requirements) or exclusions is provided.

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