Code Tools
Format, minify and test your code — private, in your browser
Beautify and minify HTML, CSS, JavaScript, TypeScript and SQL, test regular expressions, explain cron schedules and convert curl commands. 13 free tools that never upload your code — no signup, no limits.
All code tools
Popular tools
- HTML FormatterIndent and tidy messy HTML with Prettier, then minify or validate it without leaving the page.
- CSS MinifierMinify CSS with csso: shorter values, merged rules, no comments, and the bytes saved shown.
- JavaScript MinifierMinify JavaScript with Terser: compress, mangle names, keep license comments and see the bytes and gzip size you save.
- SQL FormatterIndent and line-break SQL for 20 dialects, with keyword case and layout options.
Formatters & Minifiers
9 toolsHTML Formatter
Indent and tidy messy HTML with Prettier, then minify or validate it without leaving the page.
HTML Minifier
Shrink HTML by collapsing whitespace and stripping comments, with options for inline CSS and JavaScript.
CSS Formatter
Beautify CSS, SCSS or Less with Prettier, and switch to Minify or Validate on the same page.
CSS Minifier
Minify CSS with csso: shorter values, merged rules, no comments, and the bytes saved shown.
JavaScript Formatter
Beautify JavaScript and JSX with Prettier: quotes, semicolons, trailing commas and line width are yours to set.
JavaScript Minifier
Minify JavaScript with Terser: compress, mangle names, keep license comments and see the bytes and gzip size you save.
TypeScript Formatter
Format TypeScript and TSX with Prettier, check syntax with line and column, and tune quotes, semicolons and width.
SQL Formatter
Indent and line-break SQL for 20 dialects, with keyword case and layout options.
SQL Minifier
Strip comments and collapse whitespace in SQL without touching strings.
Developer helpers
4 toolsRegex Tester
Try a regular expression on your own text, see every match highlighted, preview a replace or split, and read what each part means.
Cron Expression
Turn a cron schedule into plain English, list the next 10 run times in any time zone, or build one from dropdowns.
curl to Code Converter
Paste a curl command and get JavaScript fetch, Node.js, Python, PHP, Go, Java, C# or Ruby code, or see the request broken down.
HTML Entities
Escape or unescape &, ©, © and © in either direction.
13 tools shown
Workflows
Common jobs, done in a few steps
Ship smaller pages
Minify the HTML, then the CSS, then the JavaScript, and compare the bytes saved.
Clean up a query
Format a SQL query to read it, then minify it to paste into code or a config.
Debug a pattern
Test a regular expression against sample text and check every capture group.
Call an API from code
Turn a curl command into fetch, Python, Go or another language.
Why Nelstack
Fast, private code tools
Your code never leaves your device
Source code, SQL and curl commands are processed in your browser, so proprietary code and secrets are never uploaded or stored.
Proven formatters
Formatting uses Prettier and sql-formatter, so results match what your editor plugin or CI check produces.
Clear syntax errors
Invalid code is reported with the line and column where parsing stopped, instead of silently producing broken output.
Regex that cannot hang the tab
Patterns run in a background worker with a two-second timeout, so catastrophic backtracking is stopped and reported.
No caps or signup
No daily quota, no account and no watermark on anything you format or minify.
Built for phones too
Input comes first on small screens, with touch-friendly controls and no sideways scrolling.
Looking for another kind of tool?
These live in their own tool areas and work the same private, in-browser way. JSON, YAML, XML and CSV tools live in Data Tools.
- JSON FormatterFormat and validate JSON, in Data Tools
- JSON to YAMLMove config between formats, in Data Tools
- Text Diff CheckerCompare two versions of text or code
- Base64 EncodeEncode data for APIs and configs, in Security Tools
- Hash GeneratorMD5, SHA-1, SHA-256 and more, in Security Tools
- Data ToolsConvert JSON, CSV, Excel, YAML, XML and TOML
Code Tools FAQ
Are these code tools really free?
Yes. The formatters, minifiers, regex tester, cron explainer, curl converter and HTML entity tool are free with no signup, no daily limit and no watermark. Use them as often as you like.
Is my code uploaded anywhere?
No. Every tool runs in your browser, so your source code, SQL, regular expressions and curl commands are processed on your device and are never sent to a server or stored. That makes them safe to use with proprietary or internal code.
What actually formats my code?
Formatting is done by established open-source libraries running locally: Prettier for HTML, CSS, JavaScript and TypeScript, and sql-formatter for SQL. The output follows the same rules as those tools, so it matches what an editor plugin or a CI check would produce with the same settings.
Can minifying change how my code behaves?
Usually not, but it can. Minifiers rename variables and drop unused code, which breaks scripts that rely on function names, eval or reading source text, and aggressive CSS restructuring can reorder rules. Each minifier has options to switch those steps off, and you should test the minified output before shipping it.
How does the regex tester avoid freezing the page?
The regex tester runs your pattern in a background worker with a two-second timeout. A pattern that backtracks catastrophically is stopped and reported instead of hanging the tab, and it uses the JavaScript regular expression engine, so results match what your browser or Node.js would do.
Are my curl commands and secrets safe, and where are the JSON, YAML and CSV tools?
A curl command with tokens or passwords in it is parsed locally and never leaves your device, so headers and credentials stay private. For JSON, YAML, XML and CSV formatting and conversion, use Data Tools, which works the same private way.