---
title: "JMeter Regex Extractor Builder"
description: "Paste an HTTP response and get Regular Expression Extractor fields for tokens, CSRF, and UUIDs. Browser-only analysis; nothing is uploaded. Max 1 MB."
url: https://docs.jmeter.ai/tools/regex-tester/
lastUpdated: 2026-10-01
source: docs.jmeter.ai
---

# JMeter Regex Extractor Builder

Paste a response body. The tool scans for likely **dynamic values** (tokens, CSRF fields, UUIDs, JWTs) and proposes **Regular Expression Extractor** settings you can copy into JMeter.

## Privacy and limits

| Rule | Detail |
| --- | --- |
| **Where it runs** | 100% in your browser (this page). |
| **What is sent** | Nothing: no upload, no server analysis. |
| **Max body size** | **1 MB** (1,048,576 bytes). Larger pastes are rejected so the tab stays responsive. |
| **Scope** | **Regular Expression Extractor** only (not JSON Extractor / Boundary Extractor). |

## Extractor field mapping

| JMeter field | This tool |
| --- | --- |
| Name of created variable | Suggested from key / type |
| Regular Expression | Generated pattern with one capture group |
| Template | `$1$` |
| Match No. | `1` (first match) |
| Default Value | `NOT_FOUND` |

## Tips

- Prefer **JSON Extractor** when the entire body is JSON; more stable than regex.
- Always verify with a **Debug Sampler** or View Results Tree; browser JS RegExp is close to Java but not identical.
- If nothing is found, paste a **smaller fragment** that still includes the token and its key.

## Related reading

- [Regular Expressions](/user-manual/regular-expressions/)
- [Functions and Variables](/user-manual/functions/)
- [HTTP Recorder](/topics/http-recorder/)
- [Component Reference](/user-manual/component-reference/)

## Continue Learning

→

### Next Practical Step

Add a Regular Expression Extractor under your sampler, paste the fields, then confirm with a Debug Sampler.

📖

### Related Reference

[Functions guide](/topics/functions-and-variables/) · [Best practices](/user-manual/best-practices/)

⚠

### Common Mistakes

Using Match No. 0 (random) in load tests when you need a stable extraction.

🔧

### Troubleshooting

No candidates? Paste a smaller fragment that still includes the token.