DevFormatter

Free Online Developer Formatter Tools

Instant formatter and validator tools for developers. No signup, no server.

🔒 Runs in your browser · ⚡ No network round trips · 🆓 Free, no account · 📶 Works offline

Formatters

Format, validate, and minify JSON instantly in your browser.

Format, validate, and convert YAML instantly in your browser.

What are the most common JSON errors?: Trailing commas ({"a":1,} is invalid), single-quoted strings (JSON requires double quotes), unquoted keys, and comments (JSON has no comment syntax). The JSON Formatter reports the exact line and column of any error.
What are the most common YAML errors?: Tab characters for indentation (YAML only allows spaces), inconsistent indentation levels, and missing colons after mapping keys. The YAML Formatter highlights the exact line.
Why does my YAML behave differently in Docker Compose or GitHub Actions?: Both use YAML 1.1 parsers, which silently convert bare yes, no, on, off to booleans and time-like values like 22:30 to integers. Use the YAML Formatter's Fix YAML 1.1 Risks button to auto-quote these values.
JSON or YAML — which should I use?: JSON for data sent between systems — APIs, webhooks, config read by machines. YAML for files humans write and maintain — it supports comments, multi-line strings, and anchors. Both tools can convert between the two formats in one click.