Send new fmsg message

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

Annotations already mark this as destructive and non-idempotent, but the description adds critical context: messages cannot be edited or recalled, secrets are redacted with a count reported, and host rejection reasons are returned verbatim. These behavioral traits go well beyond what readOnlyHint/destructiveHint convey.

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 front-loaded with the primary action, followed by the most important safety caveat, then formats, redaction, error behavior, and the sibling alternative. Every sentence contributes meaning without repetition or 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?

For a destructive, non-idempotent messaging tool, the description covers the action, immutability risk, recipient format, body format, secret handling, error behavior, and sibling routing. Parameter details are largely covered by the schema, and an output schema exists, so no critical operational context is missing.

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 71%, so the schema carries most parameter meaning. The description adds valuable semantics for the key parameters: recipient address formats ('full @user@domain addresses or resolvable short names'), Markdown default for the body, and secret-redaction behavior affecting the body. This elevates 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 opens with a clear verb and resource: 'Send a new message immediately, starting a new thread.' It explicitly contrasts itself with reply ('To continue an existing conversation use reply instead'), so an agent can distinguish it from the most likely sibling without inspecting schemas.

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 when-to-use guidance: only send 'when the user has clearly asked to' because messages are immutable. It also names the alternative (reply) for continuing an existing conversation, making the selection condition unambiguous.

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