# Regex tester

- Human page: https://happytails.ai/en/developer-tools/regex-tester/
- Markdown: https://happytails.ai/en/developer-tools/regex-tester.md
- Structured JSON: https://happytails.ai/agents/en/developer-tools/regex-tester/index.json
- Visibility: public

## Tool capabilities

| Property | Value |
| --- | --- |
| Tool ID | `regex-tester` |
| Category | developer-tools |
| Implementation | Registered implementation. Registration alone is not a production-quality guarantee. |
| Browser execution | Use the visible action or interactive controls. |
| Browser processing | Browser; see tool notes for network behavior. |
| HTTP API | Not callable through HTTP. |
| Browser-agent interface | run_current_tool |

### Implementation notes

JavaScript regular expressions run in a disposable worker with a 1-second limit and maximum 10,000 matches.

### Inputs and settings

Text input: Your text.

Example or placeholder shown in the interface (not a validated fixture):

```text
Type or paste your input…
```

Up to 1,000,000 characters. Review the settings before running.

| Setting | Meaning | Control type | Default | Constraints |
| --- | --- | --- | --- | --- |
| `pattern` | Regular expression | text | "\\b\\w+\\b" |  |
| `flags` | Flags | text | "g" |  |

### Browser-agent workflow

1. Open the human page in a browser that supports WebMCP.
2. Discover the interface exposed by that page; use its actual schema.
3. Select files on the page first when the tool requires files.
4. Call `run_current_tool` with valid input and settings.
5. Inspect the returned result or error and the displayed output. Retrieve files from the displayed download links.

Calls do not automatically copy or download results. Browser permissions still apply. Interface availability alone is not proof of successful execution.

### Planning specification

Declare JavaScript flavor and flags; show groups; interrupt pathological expressions.

This describes intended requirements. Use the implementation notes, interface schema and observed output to determine current support.

### Complete machine-readable capability record

```json
{
  "id": "regex-tester",
  "category": "developer-tools",
  "built": true,
  "requirements": "Declare JavaScript flavor and flags; show groups; interrupt pathological expressions.",
  "implementation": {
    "fields": [
      {
        "key": "pattern",
        "label": "Regular expression",
        "value": "\\b\\w+\\b",
        "type": "text"
      },
      {
        "key": "flags",
        "label": "Flags",
        "value": "g",
        "type": "text"
      }
    ],
    "note": "JavaScript regular expressions run in a disposable worker with a 1-second limit and maximum 10,000 matches.",
    "experience": {
      "automatic": false,
      "single": false,
      "label": "Your text",
      "placeholder": "Type or paste your input…",
      "help": "Up to 1,000,000 characters. Review the settings before running.",
      "action": null
    },
    "mode": "explicit",
    "interactive": false
  },
  "execution": "Browser interface",
  "api": null,
  "browser_agent": {
    "supported": true,
    "name": "run_current_tool",
    "discovery": "WebMCP on the human page in a supporting browser",
    "verification": "See audit/API-AUDIT.md; availability is not verification"
  }
}
```

## Page guide

Declare JavaScript flavor and flags.

## Useful next steps

- [Find and replace](https://happytails.ai/en/text-tools/find-and-replace/): Replace every exact match with your chosen text. ([Markdown](https://happytails.ai/en/text-tools/find-and-replace.md))

- [Extract urls](https://happytails.ai/en/text-tools/extract-urls/): Find unique HTTP and HTTPS links in pasted text. ([Markdown](https://happytails.ai/en/text-tools/extract-urls.md))

- [JSON validator](https://happytails.ai/en/developer-tools/json-validator/): Line/column errors and clear syntax-versus-schema validation scope. ([Markdown](https://happytails.ai/en/developer-tools/json-validator.md))

## How to use Regex tester

1. Enter your text in the input field.
2. Review the settings, then choose Run Regex tester.
3. Review the result, then use Copy result or a download link when available.

## Working with regex tester

Formatting makes existing data or code easier to read. Validation checks whether it follows a syntax or schema. Conversion maps it into another representation. Choosing the right operation helps avoid treating a neatly formatted result as proof that the underlying data is correct.

## Common questions

### Does valid JSON mean the data is correct?

Syntax validation only establishes that the text can be parsed as JSON. A schema can check required fields and types, but neither proves that an email address, price or external record is factually correct.

### Is decoding the same as decrypting or verifying?

No. Base64 and URL encoding are representations, not encryption. Reading a token payload does not verify its signature. Use the specific validation or verification process required by the system receiving the result.

Continue your workflow: [Find and replace](https://happytails.ai/en/text-tools/find-and-replace/), [Extract urls](https://happytails.ai/en/text-tools/extract-urls/), [JSON validator](https://happytails.ai/en/developer-tools/json-validator/).