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 this is an update operation but doesn't mention permission requirements, whether changes are reversible, what happens to unspecified fields, or how conflicts are handled. The 'omit to keep existing' note is useful but insufficient for a mutation tool with zero annotation coverage.

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?

Well-structured with a clear opening sentence followed by parameter explanations. Every sentence adds value, though the parameter explanations could be slightly more concise. The formatting with 'Args:' section makes it easy to scan.

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 this is a mutation tool with no annotations but with an output schema (which handles return values), the description is moderately complete. It covers the basic operation and parameters but lacks important behavioral context about permissions, side effects, and error handling that would be crucial for safe usage.

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 and the 'omit to keep existing' behavior. The href parameter is correctly identified as coming from calendar_list_events, adding valuable context beyond the bare schema.

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 ('Update') and resource ('existing CalDAV event'), making the purpose unambiguous. It doesn't explicitly differentiate from sibling tools like calendar_create_event or calendar_delete_event, but the 'existing' qualifier implies it's for modification rather than creation or deletion.

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?

No explicit guidance on when to use this tool versus alternatives. The description mentions the href comes 'from calendar_list_events,' which is helpful but doesn't provide comprehensive usage context. There's no mention of prerequisites, error conditions, or when to choose this over other calendar tools.

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