[Write] Add a build to a TestFlight group

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

No annotations are provided, so the description carries the full burden. It discloses the core behavior: adds the build, making it available to testers, and the prerequisite that the build must already exist. While it does not mention permissions, reversibility, or error cases, for a simple write operation the description covers the essential behavioral traits. A score of 4 is justified because it goes beyond the bare minimum with the prerequisite and exclusion, but lacks some depth.

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 concise: two sentences that pack the core action, outcome, prerequisite, and a sibling pointer. It starts with 'Write.' to immediately signal the operation type. Every sentence adds value, and there is no redundant or filler content.

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 three-parameter write tool with no output schema and no annotations, the description provides the essential context: what it does, when to use it, and what is required. It could be more complete by mentioning response behavior or error cases, but the existing information is sufficient for an agent to confidently invoke the tool. The overall context is covered well.

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?

The input schema already provides 100% coverage for the three parameters (appId, group, buildId) with meaningful descriptions. The tool description does not add any additional parameter-level semantics or syntax details beyond what the schema provides. Baseline 3 is appropriate since the schema does the heavy lifting.

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 specific action ('Adds an already-uploaded build to a TestFlight beta group') and the outcome ('making it available to that group's testers'). It also distinguishes from sibling tools by explicitly noting it does not upload builds, which sets it apart from asc_build_upload. The verb 'Adds' is unambiguous and the resource (TestFlight beta group) is precise.

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 usage guidance: the build must already exist in App Store Connect, and it directs the user to asc_builds_list for checking existing builds. It also states a clear when-not ('this tool does not upload builds'), effectively pointing to an alternative. This is a strong example of telling the agent when to use this tool versus alternatives.

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