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Agent skill

Regex Expert

by RightNow-AI in RightNow-AI/openfang

Regular expression expert for crafting, debugging, and explaining patterns

Apache-2.0Auto-check passedDevelopment

Install Regex Expert

skills CLI
$ npx skills add RightNow-AI/openfang --skill regex-expert -a claude-code

Project install by default; add -g for ~/.claude/skills/.

GitHub CLI
$ gh skill install RightNow-AI/openfang regex-expert --agent claude-code

Project scope by default; add --scope user for a personal install. Needs GitHub CLI 2.90.0 or later (public preview).

Manual copy
$ git clone --depth 1 https://github.com/RightNow-AI/openfang.git skills-src && mkdir -p .claude/skills && cp -r skills-src/crates/openfang-skills/bundled/regex-expert .claude/skills/regex-expert && rm -rf skills-src

Use ~/.claude/skills/ instead of .claude/skills for a personal install. The folder must contain SKILL.md.

Claude Code skills documentation · loads skills from .claude/skills/

Facts

Skill name
regex-expert
GitHub stars
18k
Token cost
~792 tokens
SKILL.md length
406 words
Files
1
Skills in repo
68
Repo updated
First seen
Licence
Apache-2.0

At a glance

Regular expression expert for crafting, debugging, and explaining patterns

  • Tasks that involve Debugging
  • SKILL.md covers Key Principles, Crafting Patterns, Common Patterns and Debugging Techniques, plus 2 more sections
  • Instructions only: no scripts, shell commands, URLs or credentials in SKILL.md

What it does

Regex Expert is an agent skill from RightNow-AI/openfang. Regular expression expert for crafting, debugging, and explaining patterns

Its SKILL.md is about 790 tokens, which your agent loads only when the skill is triggered. It is a single SKILL.md file with no bundled scripts.

It sits in Development, covering Debugging. The repository describes itself as: Open-source Agent Operating System. The licence is Apache-2.0.

When your agent uses it

  • Tasks that involve Debugging

Example prompts

  • “/regex-expert”

What it can do on your machine

Read from SKILL.md and the folder at commit acf2587. It shows what the files ask for, not the result of running them.

  • Tool permissions

    Pre-approves nothing: there is no allowed-tools line, so your agent's usual permission prompts apply.

    From allowed-tools in the SKILL.md frontmatter.

  • Runs code

    No scripts in the folder and no shell commands in SKILL.md.

    From the folder's file list and the shell code blocks in SKILL.md.

  • Network

    No URLs in SKILL.md.

    From URLs in SKILL.md, links to its own repository left out.

  • Credentials

    Names no API keys, tokens, secrets or passwords.

    From names ending in _API_KEY, _TOKEN, _SECRET, _KEY or _PASSWORD in SKILL.md.

Context cost

Regex Expert loads about 792 tokens when it runs. Until then it costs about 22 tokens; SKILL.md has 406 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it
~22
When it runs · the whole SKILL.md, loaded when a task matches
~792

Estimates: characters ÷ 4, the usual rule of thumb; real counts depend on the model's tokenizer. Scripts and assets cost tokens only if the agent reads them.

Safety

Auto-check passed

The automated check found no risky patterns in SKILL.md.

Automated static check — not a guarantee. Review scripts before installing. It scans the text of SKILL.md for risky patterns (piping downloads into a shell, reading credential files, hidden Unicode, destructive commands); files beside SKILL.md are not scanned.

SKILL.md

The full file from RightNow-AI/openfang at commit acf2587, republished under its Apache-2.0 licence (© RightNow-AI). 406 words, ~792 tokens.

Download SKILL.mdSave it as .claude/skills/regex-expert/SKILL.md (or your agent's skills folder).
name
regex-expert
description
Regular expression expert for crafting, debugging, and explaining patterns

Regular Expression Expert

You are a regex specialist. You help users craft, debug, optimize, and understand regular expressions across flavors (PCRE, JavaScript, Python, Rust, Go, POSIX).

Key Principles

  • Always clarify which regex flavor is being used — features like lookaheads, named groups, and Unicode support vary between engines.
  • Provide a plain-English explanation alongside every regex pattern. Regex is write-only if not documented.
  • Test patterns against both matching and non-matching inputs. A regex that matches too broadly is as buggy as one that matches too narrowly.
  • Prefer readability over cleverness. A slightly longer but understandable pattern is better than a cryptic one-liner.

Crafting Patterns

  • Start with the simplest pattern that works, then refine to handle edge cases.
  • Use character classes ([a-z], \d, \w) instead of alternations (a|b|c|...|z) when possible.
  • Use non-capturing groups (?:...) when you do not need the matched text — they are faster.
  • Use anchors (^, $, \b) to prevent partial matches. \bword\b matches the whole word, not "password."
  • Use quantifiers precisely: {3} for exactly 3, {2,5} for 2-5, +? for non-greedy one-or-more.

Common Patterns

  • Email (simplified): [a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,} — note that RFC 5322 compliance requires a much longer pattern.
  • IPv4 address: \b(?:\d{1,3}\.){3}\d{1,3}\b — add range validation (0-255) in code, not regex.
  • ISO date: \d{4}-(?:0[1-9]|1[0-2])-(?:0[1-9]|[12]\d|3[01]).
  • URL: prefer a URL parser library over regex. For quick extraction: https?://[^\s<>"]+.
  • Whitespace normalization: replace \s+ with a single space and trim.
Show full SKILL.md (187 more words)Show less

Debugging Techniques

  • Break complex patterns into named groups and test each group independently.
  • Use regex debugging tools (regex101.com, regexr.com) to visualize match groups and step through execution.
  • If a pattern is slow, check for catastrophic backtracking: nested quantifiers like (a+)+ or (a|a)+ can cause exponential time.
  • Add test cases for: empty input, single character, maximum length, special characters, Unicode, multiline input.

Optimization

  • Avoid catastrophic backtracking by using atomic groups (?>...) or possessive quantifiers a++ (where supported).
  • Put the most likely alternative first in alternations: (?:com|org|net) if .com is most frequent.
  • Use \A and \z instead of ^ and $ when you do not need multiline mode.
  • Compile regex patterns once and reuse them — do not recompile inside loops.

Pitfalls to Avoid

  • Do not use regex to parse HTML, XML, or JSON — use a proper parser.
  • Do not assume . matches newlines — it does not by default in most flavors (use s or DOTALL flag).
  • Do not forget to escape special characters in user input before embedding in regex: \., \*, \(, \), etc.
  • Do not validate complex formats (email, URLs, phone numbers) with regex alone — use dedicated validation libraries and regex only for quick pre-filtering.

© RightNow-AI, Apache-2.0. Rendered from Markdown: HTML in the file is shown as text, images as links, and headings moved down two levels. Raw file

Files

Just SKILL.md in crates/openfang-skills/bundled/regex-expert of RightNow-AI/openfang.

Open the folder on GitHubat commit acf2587

Compare with similar skills

Regex Expert next to the 5 skills that share the most tags, products or categories with it. Stars are the repository's; “used in” counts other GitHub owners with a copy.

Regex Expert compared with similar skills
SkillStarsUsed inTokensAuto-checkLicenceRepo updated
Regex Expert this skillRightNow-AI/openfang18k—~792Automated safety check: PassApache-2.0
Trellis Session Insightmindfold-ai/Trellis15k4 repos~1.7kAutomated safety check: PassAGPL-3.0
Native Data FetchingCherryHQ/cherry-studio-app4k6 repos~2.9kAutomated safety check: NotesMIT
Debugging Executionsn8n-io/n8n207k—~2.6kAutomated safety check: PassCustom licence
Aoti Debugpytorch/pytorch104k1 repos~1.7kAutomated safety check: PassCustom licence
Herdr Throwaway Reproductionherdrdev/herdr43k—~2.4kAutomated safety check: PassApache-2.0

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Categories

Questions about Regex Expert

What does Regex Expert do?

Regular expression expert for crafting, debugging, and explaining patterns. Regex Expert is an agent skill from RightNow-AI/openfang.

When should I use Regex Expert?

Regex Expert fits situations like: tasks that involve Debugging.

How do I install Regex Expert in Claude Code?

Run `npx skills add RightNow-AI/openfang --skill regex-expert -a claude-code`. Or copy the skill folder (crates/openfang-skills/bundled/regex-expert in RightNow-AI/openfang) into .claude/skills/regex-expert in your project. Claude Code loads it when a task matches its description.

How do I install Regex Expert in Codex?

Run `npx skills add RightNow-AI/openfang --skill regex-expert -a codex`. Or copy the skill folder (crates/openfang-skills/bundled/regex-expert in RightNow-AI/openfang) into .agents/skills/regex-expert in your project. Codex loads it when a task matches its description.

Can I use Regex Expert in Cursor, Gemini CLI or GitHub Copilot?

Cursor, Gemini CLI, GitHub Copilot and OpenCode also load SKILL.md folders. With the skills CLI, run `npx skills add RightNow-AI/openfang --skill regex-expert -a cursor` (or -a gemini-cli, github-copilot or opencode for the others). To copy it by hand, put the folder in .cursor/skills/regex-expert, .gemini/skills/regex-expert, .github/skills/regex-expert and .opencode/skills/regex-expert in your project.

What does Regex Expert need to run?

SKILL.md names no scripts, command-line tools or credentials: Regex Expert is instructions for the agent only.

Does Regex Expert access the network?

SKILL.md contains no URLs. Any network use would come from the scripts or tools the agent runs. This is read from the text; nothing was executed.

Is Regex Expert safe to install?

Our automated static check of SKILL.md found no risky patterns, such as piping downloads into a shell, reading credential files or hidden Unicode. It is not a guarantee. Review the folder before installing.

What licence does Regex Expert use?

Regex Expert is published under the Apache-2.0 licence (the repository's licence). It allows redistribution, so the full SKILL.md is shown on this page.

How many tokens does Regex Expert use?

About 792 tokens (SKILL.md is roughly 3.2k characters). Agents keep only the skill's name and description in context until a task matches; then they load SKILL.md in full.

What are the alternatives to Regex Expert?

Skills that share tags, products or a category with Regex Expert: Trellis Session Insight (mindfold-ai/Trellis, 15k stars), Native Data Fetching (CherryHQ/cherry-studio-app, 4k stars), Debugging Executions (n8n-io/n8n, 207k stars) and Aoti Debug (pytorch/pytorch, 104k stars). The comparison table on this page puts their stars, adoption, token cost, safety result and licence side by side.

Who maintains Regex Expert?

RightNow-AI (a GitHub organization) maintains it in RightNow-AI/openfang, which has 18,214 GitHub stars. The repository holds 68 skills in this directory. The repository was last updated on July 2, 2026.

Source: RightNow-AI/openfang on GitHub. Facts on this page come from the repository at the commit we read; the author's words are quoted as theirs.