Test a regular expression

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

With no annotations present, the description fully carries the behavioral burden. It discloses the return content (all matches, positions, capture groups), error handling for invalid patterns, and the read-only nature of the operation. This is meaningful behavioral information beyond what the schema provides.

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?

Three short sentences, each earning its place: the first states the core action and output, the second clarifies error behavior, and the third gives the intended use case. It is front-loaded and contains no filler.

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 regex-testing utility, the description provides everything an agent needs: the operation, the output shape, error handling, and the use case. There is no output schema, so the description appropriately fills that gap by explaining what the tool reports.

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 the schema already documents pattern, text, and flags. The description adds a little context by mentioning positions and capture groups, but it does not need to describe parameters further since the schema already does so adequately.

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 action ('Run a regular expression against text') and a precise output ('every match with its position and capture groups'). It also distinguishes this from sibling tools like count_text, score_readability, diff_texts, and hash_text by focusing on regex behavior rather than counting, scoring, diffing, or hashing.

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 final sentence gives a clear usage context: 'Use it to check a pattern actually does what it looks like it does.' This tells an agent when the tool is appropriate, though it does not explicitly name alternative tools or state when not to use it. The context is clear enough that an agent can route to this tool for regex verification.

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