Run Python online in 10 minutes: print, loops & functions
No download, no install — learn print, variables, loops and functions with live examples in Python 3.12 right in your browser.
Python · Beginner
Evergreen SEO guides
The FastCompiler blog
Practical, timeless guides on writing search-friendly HTML, CSS and JavaScript — and testing everything before you publish.
JavaScript · Guide
JavaScript map, filter & reduce — explained with live examples
Three methods, 80% of real array work. Five runnable examples plus the filter-map-reduce interview chain.
JSON · Debugging
Fix broken JSON fast: validate, beautify & find errors
Trailing commas, single quotes, missing brackets — read line/column errors and fix 90% of JSON in seconds, offline.
CSV · Data
View CSV without Excel: filter, sort & convert to JSON
Open large CSVs, sort and filter instantly, convert to JSON — all offline, no upload, no spreadsheet install.
Beginner Guide · HTML
How to run HTML, CSS and JavaScript online
No installs, no accounts — just a browser. A step-by-step beginner's guide with a starter project you can run in a free online compiler right now.
Tool Comparison · HTML
The best free online HTML compilers, compared
CodePen, JSFiddle, FastCompiler and more — six free tools honestly compared on setup, privacy, offline use and sharing.
HTML · CSS
The <details> element: accordions and animations without JavaScript
Exclusive accordion groups with the name attribute, deep-linkable answers, and smooth JS-free animations with ::details-content — the full details element guide.
SEO · Testing
Test your meta tags and Open Graph tags before you publish
A 10-minute workflow to check your title, description and Open Graph tags in the FastCompiler preview — so search and social previews never break.
SEO · HTML
How to write SEO-friendly HTML: the tags that matter
Title tags, meta descriptions, heading structure and semantic elements — the markup search engines actually read, with copy-paste examples you can run in FastCompiler.
SEO · HTML
SEO-friendly HTML structure: headings, hierarchy & outline test
One H1, clean heading hierarchy and real landmarks — a 5-minute restructure plan with live code you can run.