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

With no annotations providing behavioral hints (readOnlyHint, destructiveHint) beyond the title, the description carries the full burden. It discloses that the tool checks HTML and runs mu.api calls server-side, implying a diagnostic operation without directly opening the app. This is meaningful behavioral detail, though it does not explicitly state whether the operation is side-effect-free or mention permissions.

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 a single, front-loaded sentence that efficiently conveys what the tool does, how it does it, and why it is useful. There is no redundant or filler language—every part adds value. It is appropriately concise for the tool's simplicity.

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 the tool has only one parameter (fully documented in the schema), no annotations, and no output schema, the description is fairly complete. It explains the action, method, and purpose, which is sufficient for an agent to understand and invoke the tool. However, it does not describe the return value or what a successful/failed test looks like, which would be helpful context.

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 single 'slug' parameter with a clear description ('The app's URL slug'). The tool description adds no additional meaning about the parameter—it does not explain slug format, where to find it, or any constraints beyond the schema. Therefore, the description does not enhance the schema's semantics.

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 tool's purpose: 'Test an app by checking its HTML and running its mu.api calls server-side.' It uses a specific verb ('Test') and resource ('app'), and explains the mechanism (checking HTML, running mu.api calls) and the intended outcome (finding what is broken). This distinguishes it from sibling tools like apps_read or apps_run.

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 gives a clear context for when to use the tool: 'so an author finds out what is broken without opening it.' However, it does not explicitly mention when not to use it or provide alternative tools. There is no direct comparison with siblings such as apps_run or apps_read, so the usage guidance is implied rather than explicit.

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