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 of behavioral disclosure. It mentions the partial update behavior ('Only the fields you provide will be changed'), which is useful. However, it doesn't cover critical aspects like whether this is a mutation (implied by 'update'), authentication requirements, error handling, rate limits, or what the output contains. For a mutation tool with zero annotation coverage, this leaves significant gaps.

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 and appropriately sized: a clear purpose statement, a key behavioral note, and a parameter list. Every sentence adds value, with no redundant information. It could be slightly more front-loaded by integrating the parameter semantics 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's complexity (mutation with 6 parameters), lack of annotations, and presence of an output schema, the description is moderately complete. It covers the purpose and partial update behavior, and the parameter list helps compensate for low schema coverage. However, it misses behavioral details like error cases or output expectations, and the output schema's existence means the description doesn't need to explain return values, but more context would improve 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 lists all 6 parameters with brief explanations (e.g., 'href: The href/URL path of the vCard resource (as returned by contacts_list)'), adding meaningful context beyond the schema's titles. However, it doesn't detail format constraints (e.g., email validation) or provide examples, preventing a perfect score.

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 tool's purpose: 'Update an existing contact in a CardDAV address book.' It specifies the verb ('update'), resource ('contact'), and context ('CardDAV address book'), which is specific and actionable. However, it doesn't explicitly differentiate from sibling tools like 'contacts_create_contact' or 'contacts_get_contact' beyond the 'update' verb, preventing a perfect score.

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 some implied usage guidance by stating 'Only the fields you provide will be changed; omitted fields are left as-is,' which suggests when to use this tool for partial updates. However, it lacks explicit guidance on when to use this tool versus alternatives (e.g., 'contacts_create_contact' for new contacts or 'contacts_delete_contact' for removal), and doesn't mention prerequisites like needing the 'href' from 'contacts_list'.

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