React to fmsg message

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

Discloses the side effect ('Sends a small reaction message to the other participants'), the state-changing semantics (one reaction per person; new emoji replaces previous), and failure conditions. This adds substantial behavioral context beyond the annotations.

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?

Two sentences, front-loaded with the core action, and every sentence contributes behavior or constraint information. No filler or repetition.

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 simple two-parameter mutation with high schema coverage and an output schema, the description covers the side effect, failure conditions, and per-person semantics. Nothing material 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?

The schema already covers 100% of parameters with descriptions, including the null-clears-reaction behavior. The description reinforces the replacement semantics but does not need to add new parameter-level detail.

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 verb ('Set or clear') with a clear resource ('your emoji reaction on a message') and adds the one-reaction-per-person replacement rule. This distinguishes it from send_message and reply without needing to open the schema.

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 clearly conveys when to use the tool and also says where it fails (drafts and terminal messages). It does not explicitly name sibling alternatives, but the purpose is clear enough that an agent can infer when reacting is the right action.

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