Developer utilities · by Firas Dib

regex101

A browser editor for writing, testing and debugging regular expressions in ten engine flavors, with a plain-English breakdown of each token, match details, substitution, unit tests and shareable saved versions.

You can watch a pattern match step by step, see why it fails, and catch catastrophic backtracking before it hits production.

API, no keyLicense unclear

Open regex101.com ↗ agent.md

For your project

Official API: Official API · Free tier
“regex101 is an interactive regular expression editor, tester, debugger, and sharing service with an OpenAPI-documented HTTP API.” regex101.com/llms.txt
Key: Not needed
“Authentication is optional for public workspaces and required when the requested workspace is private.” docs.regex101.com/application/api/
Formats: JSON
Data download: No bulk download found
License: site terms Terms cover the regex101 service; they do not say who owns regexes or generated code you write in it. Reselling or exploiting the service needs written permission.
Commercial use: Commercial use unclear
Credit: Not stated
Embedding: Embedding unclear
Using the website: Free tier

Read on regex101's own pages on Oct 23, 2026 · license or terms · API docs. Check the license page before you ship.

For your agent

A request your code or agent can make with no key:

https://regex101.com/api/library?search=email&orderBy=MOST_UPVOTES

Not open source (GitHub repo is an issue tracker only) and no free npm/PyPI package: the TypeScript regex parser is a separately licensed commercial product and self-hosting is a paid Docker-image Enterprise license. The API mainly reads/writes saved workspaces (public reads need no token; live OpenAPI at /api/openapi.yaml); matching runs in the browser, so test regexes locally in your target language.
Do not scrape or crawl the site; use the documented API or the MCP server
Never put bearer tokens in URLs or logs; private workspaces need a signed-in token
Do not resell or repackage the service without written permission

llms.txt: regex101.com/llms.txt · MCP: https://regex101.com/mcp

Paste into your agent: Read https://agentgid.com/resources/regex101/agent.md before using regex101.

What you can build

A code-review bot that links each regex in a pull request to a saved regex101 workspace for reviewers to inspect
A team snippet library that stores tested patterns as regex101 workspaces and pulls them via the workspace API
A docs plugin that turns a regex101 permalink into an inline card with the pattern, flavor and test strings

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