Set the mailbox signature

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

Annotations already cover mutability and idempotency. The description adds genuinely useful behavior beyond them: the storage location, how images become embedded, and the required setup/draft prerequisites. It stops short of describing side effects or failure behavior, but it is transparent about the key operational conditions.

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?

Three focused sentences with no wasted words. The main action is front-loaded, followed by usage guidance and an alternative workflow. Every sentence contributes new, relevant information.

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?

For a 3-parameter write tool with rich annotations, the description is nearly complete: it explains storage, usage, alternatives, and preconditions. The only minor gap is that it does not describe what a successful call returns or how errors surface, but no output schema exists and this is not critical for invoking the tool.

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 100%, so the schema already documents all three parameters. The description only loosely maps to html/text with 'HTML and/or text' and adds no new parameter-level detail, which matches the baseline for fully-covered schemas.

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 states a specific verb and resource: it stores the signature as a message in the 'mailmcp-signature' mailbox folder. This concrete mechanism distinguishes it from sibling tools like get_signature and create_draft, making its purpose unmistakable.

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?

It explicitly says when to use the tool ('when the owner pastes or dictates their signature') and gives an alternative workflow for photo/logo signatures. It also names prerequisites (mailbox signature setup and draft capability), so an agent knows when this tool is applicable.

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