Add fmsg recipients

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

Adds meaningful behavior beyond annotations: recipients become thread participants, the operation is irreversible, and terminal messages are unsupported. Annotations already cover destructive and non-read-only hints, so the description's additional context is valuable.

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 short sentences, each carrying necessary information: scope, effect, and caveats. No filler or repetition of schema content.

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?

The description is complete enough for a low-complexity tool with full parameter schema and output schema. It covers eligibility, consequences, and a key failure mode, though it could hint at why openWorldHint matters for address resolution.

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 id and add_to. The description clarifies the operational effect of the recipients but does not add parameter-specific meaning beyond what the schema provides.

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?

States a specific action ('Add recipients') with a precise resource ('message that was already sent') and eligibility constraints (sent by you or received as primary recipient). This clearly distinguishes it from send_message, reply, and react.

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?

Gives clear context for when the tool applies: only to already-sent messages where the caller is a primary participant. It notes terminal messages as a failure case, though it does not explicitly name alternative tools.

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