Cleanor

Test a regular expression

regex_test

Read-onlyIdempotent

Test a JavaScript regular expression against sample text and return whether it matches, plus every match with its captured groups and index. Use to verify a pattern instead of reasoning about it in your head. Input and pattern are length-capped to keep it fast and safe.

Input Schema

TableJSON Schema

Name	Required	Description	Default
`flags`	No	Regex flags, e.g. "gi". Allowed: g i m s u y d.	g
`input`	Yes	Text to test against.
`pattern`	Yes	The regex pattern (without slashes).

Output Schema

TableJSON Schema

Name	Required	Description
`matched`	Yes	Whether the pattern matched at all.
`matches`	Yes	Each match with its start index and captured groups.
`truncated`	Yes	True if results were capped at 100.
`match_count`	Yes

Schema Changelog

Changes observed during successful MCP inspections.

Changed1 schema field changedJul 7, 2026

changedOutput schema / (root)

Previous value: -nullNew value: +{
+  "$schema": "http://json-schema.org/draft-07/schema#",
+  "additionalProperties": false,
+  "properties": {
+    "match_count": {
+      "type": "number"
+    },
+    "matched": {
+      "description": "Whether the pattern matched at all.",
+      "type": "boolean"
+    },
+    "matches": {
+      "description": "Each match with its start index and captured groups.",
+      "items": {
+        "additionalProperties": false,
+        "properties": {
+          "groups": {
+            "items": {
+              "type": [
+                "string",
+                "null"
+              ]
+            },
+            "type": "array"
+          },
+          "index": {
+            "type": "number"
+          },
+          "match": {
+            "type": "string"
+          }
+        },
+        "required": [
+          "index",
+          "match",
+          "groups"
+        ],
+        "type": "object"
+      },
+      "type": "array"
+    },
+    "truncated": {
+      "description": "True if results were capped at 100.",
+      "type": "boolean"
+    }
+  },
+  "required": [
+    "matched",
+    "match_count",
+    "truncated",
+    "matches"
+  ],
+  "type": "object"
+}

AddedJul 7, 2026

TDQS

A4.3/5.0

Behavior4/5

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

The description adds the JavaScript flavor detail and notes length caps (input and pattern) to keep it fast and safe, supplementing annotations that already signal read-only and idempotent behavior. It also states output includes matches with groups and ideas, which goes beyond annotation info.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is three sentences: purpose, usage, and safety constraint. Each sentence adds distinct value and is front-loaded with the core functionality, with no redundant wording.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness5/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a simple, read-only regex testing tool with full schema coverage and an output schema, the description covers purpose, usage, and constraints. The presence of an output schema means the description doesn't need to enumerate return value structures, and annotations cover side-effect safety.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

With 100% schema coverage, each parameter is already well-described in the schema. The description adds only a general note about length caps, which is already reflected in maxLength properties, so it provides minimal additional parameter semantics beyond the baseline.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description explicitly states the tool tests a JavaScript regular expression against sample text and returns match status, every match, captured groups, and indices. This specific verb+resource combination clearly distinguishes it from all sibling utility tools, none of which relate to regex testing.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines4/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description provides clear guidance to use this tool to verify a pattern instead of reasoning about it mentally, which implies the appropriate use case. It does not explicitly exclude any scenarios or name alternative tools, so it falls slightly short of fully explicit when/when-not guidance.

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

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