Explain a test failure

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

Since there are no annotations, the description carries the full burden of behavioral disclosure. It does well by stating that the output is a 'guess', that the analysis is 'heuristic, pattern-matched', and that it is 'Fully offline - no LLM call'. This conveys uncertainty and operational constraints clearly, though a bit more detail about output format or confidence would have made it even richer.

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?

Two sentences accomplish all necessary tasks: defining input, action, output, and an important operational constraint. The key behavioral details are front-loaded, with no wasted or repetitive wording.

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 a single parameter, absent annotations, and no output schema, the description is nearly complete: it defines the input, the output type (root cause and next step), and the heuristic/offline behavior. The only minor gap is a precise description of the return value's shape, but for this simple tool the current wording is sufficient for an agent to invoke it.

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 schema's description of errorMessage already covers 'raw error/assertion message from a failed test'. The tool description adds value by scoping the input to a 'Playwright (or similar) error message', which clarifies the expected domain. With exceptionally high schema coverage at the file level, the description's incremental input is small but relevant.

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 identifies a specific verb ('returns') and a distinct resource ('a heuristic, pattern-matched guess at the root cause and a suggested next step'). The input is scoped to 'Playwright (or similar) error messages', making it easy to differentiate from sibling tools like summarize_test_run or list_flaky_tests. An agent can understand this tool's purpose without inferring anything.

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 opening 'Given a Playwright (or similar) error message' clearly indicates when this tool should be used. However, the description does not explicitly name sibling tools as exclusions or state when not to use it, so the comparison with alternatives is left to the agent's own judgment.

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