pyfastmail-mcp

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

With no annotations provided, the description carries full burden for behavioral disclosure. It states it 'creates' a new contact, implying a write operation, but doesn't mention permissions needed, whether the operation is idempotent, error handling, or what the output contains. This leaves significant 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 well-structured with a brief purpose statement followed by a parameter list. Every sentence adds value, and it's appropriately sized for the tool's complexity. It could be slightly more front-loaded by integrating parameter details into the flow, but it's efficient overall.

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 (which handles return values) and the description covers parameter semantics well, it's moderately complete. However, as a mutation tool with no annotations, it lacks behavioral context like error conditions or side effects, which limits overall completeness.

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%, so the description must compensate. It provides clear semantics for all 6 parameters, explaining what each represents (e.g., 'Full display name', 'Email address (optional)'), which adds substantial value beyond the bare schema. The only minor gap is lack of format details for fields like email or phone.

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 ('Create a new contact') and resource ('in a CardDAV address book'), distinguishing it from sibling tools like contacts_update_contact or contacts_delete_contact. It precisely identifies what the tool does without being vague or tautological.

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 no guidance on when to use this tool versus alternatives like contacts_update_contact or contacts_list. It mentions a default for address_book_href but lacks explicit when/when-not instructions or prerequisites, leaving usage context unclear.

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