YAML and JSON Converter

Validate YAML and convert it to JSON and back in your browser with exact error lines.

Runs in your browser, files never leave your device
Free, open source, no account, no ads
Works offline after the first visit

YAML → JSON JSON → YAML

Options

Indent

YAML schema How plain yes, no, on and off are read.

YAML output style

Also Sort keys A–Z Fold YAML lines at 80 chars Safe mode: refuse custom tags

YAML input Empty

Drop a file or open .yaml, .yml or .json

JSON output

Converts as you type. Ctrl/⌘ + Enter converts now, Ctrl/⌘ + S downloads.

How it works

Paste or drop your file. Pick YAML → JSON or JSON → YAML, then paste text or drop a .yaml, .yml or .json file. It is read on your device only.
Read the result as you type. The output updates after a short pause. If something is wrong you get the line, column, a caret under the problem and a plain-language hint.
Copy or download. Choose indent, key sorting and YAML style in Options, then copy the result or save it as converted.json or converted.yaml.

Questions, answered

Is my YAML or JSON uploaded anywhere?

No. YAML and JSON Converter runs entirely in your browser. The text you paste or the file you drop is parsed in memory on your device and never sent to a server, so configs with hostnames or secrets stay private. You can disconnect from the internet and it keeps working.

Why does it say a tab or a missing space is an error?

YAML forbids tab characters for indentation and needs a space after the colon in key: value. The error box shows the exact line and column with a caret, and the Go to line button puts your cursor right there. Duplicate keys are reported too.

What happens to multiple documents, anchors and dates?

Documents separated by --- become one JSON array. Anchors and aliases (including << merge keys) are expanded into copies, with a note. Dates become ISO strings, values with leading zeros such as 007 stay strings, and integers too large for JSON numbers are kept as strings with a warning.

Is "yes" a boolean or a string?

In YAML 1.2, which this tool uses by default, yes, no, on and off are plain strings. Older YAML 1.1 parsers treat them as booleans. Switch the schema in Options if you need the old behaviour; a hint appears when your file contains such values.

Is it really free, and does it work offline?

Yes. It is open source under the MIT license, with no account, no limits and no ads. After your first visit the page is cached by a service worker, so it loads without a connection, and you can install it from your browser's menu as an app.

Was this written by AI?

Yes. YAML and JSON Converter was generated by Claude Code from a written specification inside an automated pipeline, with a test suite that runs in a real browser. The full source is on GitHub, so you can read every line before you trust it with your files.

Built by one person, given away for free

YAML and JSON Converter is a free alternative to paid tools like Online YAML parsers and YAML to JSON sites. If it earns a place in your bookmarks, a coffee keeps the updates coming.

☕ Support Or on Ko-fi