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

Annotations cover the safety profile (readOnlyHint=false, idempotentHint=true, destructiveHint=false), so the bar is lower; the description still adds the required permission, the deliberate absence of email sending, and the active-org-member precondition. It does not state the failure behavior when a userId is not an org member, which is the remaining gap.

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?

Three sentences, front-loaded with the core constraint, then parameters, then permissions, then the negative routing case. Every sentence 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 3-param mutation with no output schema and annotations already declaring idempotency and non-destructiveness, this covers preconditions, permissions, and the alternative path well. Only the error/edge behavior (non-member id, duplicate add) is left unstated.

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 only 33% (userId documented, projectId not), so the description must compensate. It does add the userId lookup source and enumerates role values, but the enum is already in the schema and it adds no meaning for projectId, so compensation is partial.

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 ... to a project') and constrains scope precisely: an EXISTING active org member, not a new invitee. This immediately distinguishes it from email-invitation flows among its many siblings.

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 explicit when-to-use (existing org member), an explicit when-not and alternative (brand-new email outside the org → use the invitation UI), a prerequisite permission (project.members.manage), and the lookup step (list_org_members first). 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.