Test a regular expression

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

Annotations already indicate readOnlyHint=true and idempotentHint=true, so the description adds detail about the return structure (matches with offsets, positional and named capture groups) and optional replacement behavior. This provides useful insight into the tool's output and mutation-free nature.

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 two sentences long, efficient, and front-loaded with the primary action. Every sentence adds value, and there is no redundancy or fluff.

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 no output schema, the description adequately describes return values: matches with offsets and capture groups, plus optional replacement output. Parameter coverage is complete. It could mention error handling or flag validation but is sufficient for an agent to understand the tool.

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 describes all 4 parameters with 100% coverage. The description adds no parameter-specific details beyond what the schema already provides, such as clarifying flag patterns or replacement syntax. The baseline of 3 is appropriate given schema coverage.

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 runs a JavaScript regex against a string and returns matches with character offsets and capture groups. It also mentions an optional replacement feature. This differentiates it from sibling tools like transform_text, which may perform general text transformations.

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 explains the tool's functionality but does not provide explicit guidance on when to use it versus alternatives, nor does it mention any exclusions. The optional replacement feature is shown, but no comparison to sibling tools like transform_text is given.

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