pyfastmail-mcp

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

With no annotations provided, the description carries the full burden. It discloses key behavioral traits: it supports standard flags and custom keywords, and requires at least one of add or remove. However, it doesn't cover permissions, rate limits, error handling, or what happens if conflicting operations are attempted (e.g., adding and removing the same label).

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 first sentence stating the purpose clearly. The subsequent sentences add necessary details without redundancy. The Args section is structured but could be integrated more seamlessly; overall, it's efficient with minimal waste.

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 moderate complexity (3 parameters, mutation operation), no annotations, and an output schema (which handles return values), the description is fairly complete. It covers purpose, parameters, and key constraints. However, it could improve by mentioning side effects or linking to sibling tools for 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?

Schema description coverage is 0%, so the description must compensate. It adds significant meaning beyond the schema: it explains what email_ids are (JMAP email IDs), provides examples for add and remove parameters, and clarifies that at least one of add or remove is required. This covers the core semantics well, though it doesn't detail constraints like maximum list sizes.

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 ('Add or remove keywords/labels') on a specific resource ('on one or more emails'), distinguishing it from sibling tools like mail_mark_email_read or mail_move_email. It uses precise verbs and identifies the target resource without being 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 implied usage guidance by mentioning 'At least one of add or remove must be provided,' which helps understand when to use the tool. However, it lacks explicit guidance on when to choose this tool over alternatives like mail_mark_email_read (which handles specific flags) or other mail_* tools, and doesn't mention prerequisites or exclusions.

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