Regular expressions are easy to get almost right, which is the dangerous kind of wrong. This skill restates your matching rule in plain words, writes a pattern for your exact flavour — JavaScript, Python, PCRE or Java — and explains every token. Then it proves the pattern with a test table of strings that should and shouldn't match. It prefers readable patterns over clever ones and anchors whole-string matches. Ambiguous cases, such as spaces inside phone numbers, are listed as decisions for you rather than silently chosen, so the regex does what you meant.
Regex builder — example input and the first lines it returns. Works in ChatGPT, Claude and Gemini.
2 Paste it into a new chatChatGPT, Claude, Gemini or Copilot.
3 Send your inputSend what you want to match.
The skill — paste this into your AI assistant
# Skill: Regex builder
You are running the "Regex builder" skill for me. I work as: Developer / data engineer. What I need from you: a tested regex for my flavour, explained token by token, with matching and non-matching examples.
## When I send you what I want to match, the regex flavour (JavaScript, Python, PCRE, Java) and a few example strings
1. Restate the rule in plain words and ask about ambiguous cases only if critical.
2. Write the regex for the stated flavour.
3. Explain each token.
4. Show a table of strings that should and should not match, with the result.
## Reply in this format
- Regex (code)
- Token-by-token explanation
- Test table: string, should match?, does match?
- Edge cases to decide
## Rules
- Prefer readable patterns over clever ones; anchor with ^ and $ when matching whole strings.
- Use only the facts I give you; mark anything you had to assume with [ASSUMPTION].
- If something essential is missing, ask me one short question, then continue.
- No preamble or filler: start with the result.
Confirm you're ready in one line, then wait for me to send what I want to match, the regex flavour (JavaScript, Python, PCRE, Java) and a few example strings.
Then sendWhat you want to match, the regex flavour (JavaScript, Python, PCRE, Java) and a few example strings. For example: JavaScript: match Indian mobile numbers, optional +91, 10 digits starting 6–9
ChatGPT
Fastest: paste the skill as your first message in a new chat, then send your input.
To keep it: open a Project, choose Instructions (or Settings → Personalization → Custom instructions for every chat) and paste it there.
To share it with a team: create a custom GPT and paste the skill into its Instructions.
In the Codex app: copy the skill's folder into ~/.codex/skills/ (or Customize → Skills → Add → Create skill).
Claude
Fastest: paste the skill as your first message in a new chat, then send your input.
To keep it: create a Project, open Project instructions and paste the skill.
As a Claude Skill: download the skill's ZIP, then in Claude open Settings → Skills → Add → Upload skill and choose the file.
Gemini
Fastest: paste the skill as your first message in a new chat, then send your input.
To keep it: open Gems → New Gem, paste the skill into Instructions and save.
Microsoft Copilot
Fastest: paste the skill as your first message, then send your input.
In Microsoft 365 Copilot, save it as a prompt or paste it into an agent's instructions to reuse it.
Any other assistant
Paste the skill as the system prompt or first message in any chat assistant (Perplexity, Meta AI, DeepSeek, Mistral, local models).
Coding agents that read the Agent Skills format (SKILL.md) can load the downloaded file from their skills folder.
Install it permanently
Upload it to Claude, add it to ChatGPT's Codex app, clone it into Claude Code, or download the SKILL.md for any agent. Full guide with screenshots →
Download the ZIP and upload it in Claude. Claude then uses the skill on its own whenever a request matches.
Claude Code: save it as ~/.claude/skills/regex-builder/SKILL.md.
Claude apps: use the Claude app tab — it has a ready-made ZIP.
Other agents: place the folder wherever your tool loads Agent Skills from.
Repositoryscienceofapps.com/skills/ai-skills.git · all 200 skills, one folder each, plain git over HTTPS
What it does
The steps it follows
Restate the rule in plain words and ask about ambiguous cases only if critical.
Write the regex for the stated flavour.
Explain each token.
Show a table of strings that should and should not match, with the result.
What you get back
The reply format
Regex (code)
Token-by-token explanation
Test table: string, should match?, does match?
Edge cases to decide
Rules it never breaks
Prefer readable patterns over clever ones; anchor with ^ and $ when matching whole strings.
Uses only the facts you give it and marks assumptions.
FAQs
Questions about Regex builder
What does the Regex builder skill do?
Regular expressions are hard to write and harder to read, and one wrong character silently matches too much. The skill fixes that: a tested regex for your flavour, explained token by token, with matching and non-matching examples.
How do I install Regex builder in ChatGPT, Claude or Gemini?
Copy the skill and paste it as the first message of a new chat, then send your input. To keep it, paste it into a ChatGPT Project or custom GPT, a Claude Project or a Gemini Gem, or upload the SKILL.md file as a Claude Skill.
What do I send Regex builder after installing it?
Send what you want to match, the regex flavour (JavaScript, Python, PCRE, Java) and a few example strings. If something essential is missing, the skill asks you one short question and then continues.
Is the Regex builder skill free?
Yes. It's free to copy, use and adapt, with no sign-up, and works in the free versions of ChatGPT, Claude, Gemini and Copilot.
60 research-backed principles in 6 categories — what each one means, why it works on the human brain and how to use it on your own screens. Written by Sushant Singh, founder of Science of Apps, who has scaled consumer apps to lacs of users and spent 10+ years leading product across startups and digital businesses in the US, EU & India.
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![Regex builder AI skill for Developer / data engineer: you paste "JavaScript: match Indian mobile numbers, optional +91, 10 digits starting 6–9" and get "/^(?:\+91[- ]?)?[6-9]\d{9}$/"](/skills/img/regex-builder-ai-skill.jpg)
