slack_add_reaction

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

Annotations already declare non-readOnly, idempotent, non-destructive. The description adds real value beyond them: the reaction is posted as the authenticated user and requires the reactions:write scope, which is auth context an agent needs. It stops short of noting side effects like notifications to the message author.

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?

Four tight lines, each doing work, with the critical 'AS THE USER' scoping front-loaded. The trailing newline and slightly clipped last fragment cost a little polish but nothing is wasted.

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?

The output schema handles return values and annotations cover safety, but with 4 required parameters at 0% schema coverage the description leaves 'workspace' completely undefined and only indirectly defines channel_id. That omission matters for a call that will fail without a valid 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 coverage is 0%, so the description must carry parameter meaning. It explains ts ('message timestamp') and name ('emoji name without colons, e.g. eyes') well, but punts channel_id to another tool's docs and says nothing at all about the required 'workspace' parameter.

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 and resource ('Add an emoji reaction to a message'), names the underlying API operation, and clarifies the acting identity ('AS THE USER'). This cleanly separates it from slack_remove_reaction and slack_get_reactions 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?

Usage is implied by the operation but there is no explicit guidance on when to prefer this over alternatives or any preconditions beyond the scope requirement. An agent can infer the use case, but nothing is spelled out.

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