React to a message

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

With no annotations, the description carries the full burden. It discloses the one-reaction-per-message-per-participant constraint and the 'already reacted' failure, which are non-obvious behaviors. It implies a mutation via 'add'. However, it does not mention other side effects like authorization or reversibility, leaving a small gap.

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 deliver the action, the source for the key parameter, and the critical constraint—all front-loaded with zero waste. The structure is compact and information-dense.

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 mutation with no annotations, the description covers the key behavioral nuance (duplicate failure) and parameter sourcing. It does not describe the success output, but without an output schema that's not strictly required. Minor omissions like permissions are acceptable given the tool's simplicity.

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 value by explicitly directing the agent to read_messages for message_id, which is a practical hint. It does not augment the reaction parameter, but the schema already explains emoji/short text, so the extra guidance justifies a 4.

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 clearly identifies the action (add an emoji reaction), the target (a message in an oase), and the context. It distinguishes itself from siblings like send_message (creating a message) and update_message (editing a message) by specifying the reaction operation.

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 tells the agent to obtain message_id from read_messages output, providing a clear usage context. It doesn't explicitly list alternatives, but the action's specificity makes when-to-use unambiguous. A brief statement about not being for editing or deleting could push to 5, but the guidance is adequate.

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