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 default behavior for the address_book_href parameter, which adds some context, but fails to describe critical traits like whether this is a read-only operation (implied by 'List' but not explicit), potential pagination or rate limits, authentication requirements, or what the output looks like. For a tool with no annotations, this leaves significant gaps in understanding its behavior.

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, with the core purpose stated first ('List contacts in a CardDAV address book.') followed by parameter details. There's no wasted text, and the structure is clear, though it could be slightly more polished (e.g., integrating the Args section more seamlessly).

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 low complexity (1 parameter, no nested objects) and the presence of an output schema (which handles return values), the description is somewhat complete. It covers the basic purpose and parameter semantics adequately. However, with no annotations and minimal behavioral context, it lacks depth for a tool that interacts with address books, leaving gaps in understanding operational constraints.

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 schema description coverage is 0%, so the description must compensate. It adds meaning by explaining that address_book_href is a 'URL path of the address book' with an example and notes it defaults to the first address book found. This clarifies the parameter's purpose and default behavior beyond the schema's basic type information. However, it doesn't cover other potential aspects like format constraints or error cases, keeping it at a baseline level.

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 ('contacts in a CardDAV address book'), making the purpose immediately understandable. It distinguishes from sibling tools like contacts_get_contact or contacts_list_address_books by focusing on listing contacts rather than retrieving individual contacts or listing address books. However, it doesn't explicitly differentiate from other list operations like calendar_list_events or files_list, which keeps it from 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 no guidance on when to use this tool versus alternatives. It doesn't mention prerequisites (e.g., needing an address book first), compare it to other list tools on the server, or specify scenarios where it's appropriate. The only contextual hint is the default behavior for the parameter, which is minimal guidance.

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