Add a user to a group

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

No annotations are present, so the description fully handles transparency. It discloses idempotency (409 on re-add), error on archived group (409), email resolution, and return value (membership row id). This goes beyond basic functionality.

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?

The description is extremely concise, with four sentences covering action, parameter usage, return value, and idempotency. No excess verbiage; every sentence is informative.

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?

Given 3 parameters and no output schema, the description covers the return value, error cases, and parameter usage. It is nearly complete, though mentioning what happens with an invalid group UUID (e.g., 404) would be helpful.

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 only 33% (only id described). The description compensates by explaining the mutual exclusivity of user_id and email and that email is resolved to user_id. This adds significant meaning beyond the schema.

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 states the action ('Add a user to a user group') and specifies the two identification methods (UUID or email). It distinguishes from siblings like group_remove_member by the verb 'add'.

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?

The description provides explicit guidance: 'Provide exactly ONE of user_id/email'. It also notes idempotency and error cases, but does not compare with alternative tools or state when not to use.

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