fastmail_send_email

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

With no annotations provided, the description carries the full burden and does well: it discloses the draft-first default, the configurable FASTMAIL_DRAFT_BY_DEFAULT behavior, the server-side FASTMAIL_FOOTER_HTML appending, and the prohibition on AI self-identification. It does not mention error handling or rate limits, but the key behavioral traits that affect invocation are transparent.

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 compact and well-structured: a clear one-sentence purpose, followed by an IMPORTANT directive on draft-vs-send behavior, then succinct identity/signature rules. Every sentence carries meaningful operational guidance, with no filler.

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 8 parameters, no output schema, and no annotations, the description covers the critical context: when to draft vs send, identity constraints, signature policy, and footer behavior. It doesn't describe return values or failure modes, but those are not essential for correct invocation and schema already documents parameters fully.

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 coverage is 100%, so the baseline is 3. The description adds extra meaning by explaining the saveDraft default preference and tying the from field to the account's own identity, which goes beyond the schema text. This lifts it above the baseline.

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 action: compose and send (or save as draft) an email from the account's own Fastmail identity. This clearly differentiates it from sibling tools like fastmail_list_emails, fastmail_get_email, and masked-email management tools, leaving no ambiguity about what this tool does.

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 gives explicit, actionable guidance: default to draft unless the context implies immediate send (explicit instruction, routine automated alert, or established-contact follow-up). It also clearly instructs to send as the account owner and never add AI/agent signatures, with server-side footer configuration noted.

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