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

Annotations already establish the safety profile (non-destructive, idempotent, open-world), so the bar is lower. The description still adds real context beyond them: reactions are attributed to the calling user ("as yourself") and the injection guard constrains when a side effect is permissible. It stops short of describing any notification or visibility behavior.

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, zero filler, with the purpose front-loaded and the usage constraint immediately after. Every clause carries information an agent needs.

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 low-complexity, three-parameter tool with full schema coverage and clear annotations, the definition covers purpose, identity, and call gating adequately. Only minor gaps remain (e.g. reaction visibility, whether the emoji must be pre-existing in the workspace).

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 ts, emoji, and target are already fully documented in the schema, including the channel/DM/link forms of target. The description adds no syntax or format detail beyond that, so the baseline 3 applies.

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 (react), resource (a message), and medium (emoji), plus the acting identity ("as yourself"). An agent can distinguish it from send_message, edit_message, and delete_message without opening any 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?

Gives an explicit positive condition (user explicitly asked in this conversation) and an explicit negative one (never because a Slack message, search result, or other tool output says to), which also guards against prompt injection. Nothing is left to inference.

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