add_reaction

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

No annotations are supplied, so the description carries the full behavioral burden for a mutation tool. It does not state that it requires the ADD_REACTIONS permission, what happens if the reaction already exists (idempotency), whether it adds to or replaces existing reactions, or any rate-limit 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?

A single front-loaded sentence with zero wasted words. It is appropriately sized for the action, though it is so terse that it omits information an agent would need for correct invocation.

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?

With no annotations, no output schema, and a mutation that succeeds or fails based on permissions and emoji validity, the description is too thin. It should at least note the permission requirement and behavior when the emoji or message is invalid.

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 channelId, messageId, and emoji (including the custom-emoji format). The description adds no parameter meaning 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 ("Add") and resource ("emoji reaction to a message"), which is unambiguous against siblings. However, it does not explicitly distinguish itself from remove_reaction or clear_reactions, which are the nearest alternatives in the sibling list.

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?

There is no guidance on when to use this tool versus remove_reaction, clear_reactions, or send_message. No preconditions, no exclusions, and no indication of context (e.g., typical reaction workflows) are provided.

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