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 mentions filtering capabilities but doesn't describe critical behaviors: whether this is a read-only operation, if it requires authentication, what pagination or rate limits exist, or what happens when no filters are applied. The description is minimal and lacks 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 appropriately sized and front-loaded: the first sentence states the core purpose, followed by a structured 'Args:' section. There's no wasted text, though the formatting with line breaks could be slightly more compact. Every sentence adds value.

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 2 parameters with 0% schema coverage and no annotations, the description does adequately explain parameter semantics. However, it lacks behavioral context (read-only vs. mutation, auth needs) and doesn't mention the existence of an output schema. For a list tool with filtering, this is minimally viable but leaves gaps in operational understanding.

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 successfully adds meaning for both parameters: 'domain' is explained as 'Filter by forDomain (partial match)' and 'state' is clarified with specific enum values ('enabled', 'disabled', 'deleted', 'pending'). This provides essential semantic context missing from the schema's generic titles.

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: 'List masked email addresses' with optional filtering. It specifies the verb ('List') and resource ('masked email addresses'), making the function unambiguous. However, it doesn't differentiate from sibling tools like 'mail_list_identities' or 'mail_list_mailboxes' beyond the resource type.

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 mentions filtering options but doesn't explain when filtering by domain or state is appropriate, nor does it reference sibling tools like 'mail_search_emails' or 'mail_update_masked_email_state' that might overlap in functionality. Usage context is implied but not explicit.

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