JSON Validator
Check whether your JSON is valid and pinpoint the exact error.
Validate JSON in seconds and catch syntax issues before your application fails on a malformed payload.
What is this tool?
JSON validation confirms that a string is valid JavaScript Object Notation before you pass it into an API, a browser app, or a config loader. Even small syntax errors can break parsing completely, which makes validation one of the quickest debugging steps when a response or file looks mostly correct but fails unexpectedly. In practical work, validation is often used for API testing, config validation, and debugging payloads from backend services.
Example
Valid JSON
This parses successfully.
{"project":"cassidor","version":1,"enabled":true}Invalid JSON
This has a trailing comma and will fail parsing.
{"project":"cassidor", "version":1,}Why use Cassidor?
- Shows whether the document is valid before you ship it.
- Works directly in the browser without requiring a server.
- Makes syntax debugging faster for API and config workflows.
Frequently asked questions
What does JSON validation check?
It confirms the document is syntactically valid and can be parsed without errors.
Why does my JSON fail even though it looks fine?
Common causes include trailing commas, single quotes instead of double quotes, or missing closing brackets.
Can I validate large payloads?
Yes, if the document is valid and the browser can handle it, the tool can parse it locally.
Does validation guarantee correct application logic?
No. It confirms syntax validity, not whether the data matches the expected schema or business rules.
Related tools
Format JSON instantly in your browser. Paste a payload, tidy the structure, and copy or download the result without affecting the data itself.
Shrink JSON down to a compact format for payloads, testing, storage, or network transmission while keeping the data intact.
Compare two JSON payloads to see exactly what changed before merging or deploying an update.
Convert JSON to YAML for configuration files, readable output, or easier handoff between tools and systems.