test_regexRun a JavaScript regex against text to list each match with its position and capture groups, up to 200 matches within 0.5 seconds.
Run a JavaScript regular expression against text and list every match with its position and capture groups (up to 200 matches, 0.5 s limit).
| Name | Required | Description | Default |
|---|---|---|---|
| text | Yes | ||
| flags | No | JavaScript flags such as gi | g |
| pattern | Yes | Pattern without slashes |
Changes observed during successful MCP inspections.
v1.0.0Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnlyHint=true, destructiveHint=false and openWorldHint=false, so the safety profile is covered. The description adds genuinely non-obvious operational context: a 200-match cap and a 0.5 s execution limit, which tell the agent results may be truncated and that catastrophic backtracking will time out.
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?
One sentence, zero waste, with the action and result front-loaded before the limiting constants. Everything stated earns its place.
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 carries the return-value burden and does so well by naming matches, positions and capture groups, plus truncation and time limits. The only gap is unspecified behavior on invalid patterns or zero matches, which is minor for a 3-parameter 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 coverage is 67%, with pattern and flags already documented ("Pattern without slashes", default "g", "JavaScript flags such as gi"). The description reinforces the JavaScript dialect, which matters for flag and syntax expectations, but says nothing beyond the schema about text handling. 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?
States a specific verb (Run) plus resource (JavaScript regular expression against text) and describes the exact output (every match with position and capture groups). No sibling tool does regex testing, and the JS-regex dialect qualifier separates it from generic text utilities like count_words.
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?
Usage is implied by the phrase "against text and list every match," so an agent can infer the testing/scanning scenario. However, there is no explicit when-to-use guidance, no note on invalid-pattern behavior, and no mention of when another sibling (e.g. count_words, hash_text) would be preferable.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.