Regex test / match / extract / replace (safe)

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

With no annotations provided, the description carries the full burden. It discloses the catastrophic-backtracking protection, killable worker, hard timeout, and the fact that pathological patterns return a 400 instead of hanging. This adds meaningful behavioral context beyond the raw schema.

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 entire description is one concise sentence that leads with 'FREE' and the safety guarantee, then immediately notes op types and relevant args. Not a wasted word, and the structure is easy to parse.

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?

The schema covers all parameters and the description adds safety context, but there is no output schema and the description does not explain what each op returns (e.g., boolean for test, match list, replacement string). For an AI agent, this leaves some ambiguity about expected return values.

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 already covers 100% of parameters with descriptions, so the baseline is 3. The description's 'Args' summary restates op, flags, and replacement but does not add deeper semantics beyond what the schema already provides. It omits the limit parameter entirely, though that is also in the schema.

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 opens with 'Run a regular expression against input' and the title enumerates 'test / match / extract / replace', giving a specific verb+resource. This clearly distinguishes it from sibling tools like encode, convert, and text, which handle other text operations.

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 conveys usage through the op parameter (test|match|extract|replace) and the safety note, but it never explicitly states when to prefer this tool or what alternatives exist. Usage is implied by the tool's function rather than stated as guidance.

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