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, and it only discloses accepted emoji input formats. It says nothing about permission requirements, whether duplicate reactions are idempotent or error, or whether the reaction is applied on behalf of the authenticated user.

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 short sentences, front-loaded with the action and followed by the input format caveat. It is efficient, though the second sentence partly duplicates the emoji_name schema description rather than adding new information.

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 write tool with a fully documented schema, the description is adequate to call it correctly. However, with no annotations and no output schema, it leaves the agent without any signal about failure modes or return behavior, which is a real gap for a mutation tool.

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 both post_id and emoji_name are already documented with examples, and the description's format examples largely restate what the schema says. The emoji character example ("👍") adds a small amount of clarity beyond the schema but no new meaning for post_id.

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 gives a specific verb and resource ("Add an emoji reaction to a message"), which naturally separates it from the sibling tools remove_reaction and get_reactions. It stops short of naming those siblings explicitly, so differentiation is inferred from the verb rather than stated.

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?

Usage is implied by the verb 'Add' — an agent can infer this is the write counterpart to remove_reaction and get_reactions — but the description never states when to use it, prerequisites such as channel membership, or what to do if the reaction already exists.

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