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

Annotations only declare readOnlyHint=true and openWorldHint=false. The description adds meaningful behavioral context: sandboxed execution, a 250ms kill switch against catastrophic backtracking, and the JavaScript/ECMAScript dialect. This goes beyond what annotations imply and informs the agent of important runtime constraints.

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 three sentences, all high-signal: what it does, why to use it, and safety/dialect caveats. No redundant phrasing or filler. It is front-loaded with the action and result.

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?

With no output schema, the description explicitly lists the returned match components (text, indices, capture groups, named groups, replacement), which covers return value expectations. It also covers execution constraints and dialect, making the tool's behavior fully understandable for a test utility.

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 100%, so all four parameters already have clear meanings. The description does not add significant details beyond what the schema provides—it only mentions 'optional replacement output' which the schema already explains. Baseline 3 is appropriate.

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 states a specific verb ('Execute') and resource ('regex against test strings'), and enumerates the exact outputs: match text, indices, capture groups, named groups, and optional replacement. This clearly distinguishes it from all sibling tools, which are unrelated (timers, network, key-value, etc.).

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 phrase 'Deterministic proof, not prediction - run this before shipping a pattern' gives clear context that this is for verifying regex patterns prior to deployment. It doesn't explicitly name alternatives or exclusions, but no competing sibling exists for regex testing, so the guidance is sufficient.

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