JSON Validator
Check JSON for syntax errors with precise error reporting. Identifies invalid tokens, mismatched brackets, trailing commas, unquoted keys, and other common JSON mistakes before they reach your application.
Parses JSON strictly according to RFC 8259 and reports the first syntax error found.
Identifies common mistakes like trailing commas and single-quoted strings.
Reports the character position or line of the error for quick debugging.
Returns a clear valid confirmation when JSON passes all checks.
Works with any JSON structure: objects, arrays, primitives, and nested combinations.
How to Use
Paste your JSON string into the input field
The validator parses it and reports valid or the specific error
Fix the indicated issue in your JSON source
Re-validate until the JSON passes cleanly
Debugging
- Check API payloads that fail to parse
- Validate hand-edited config files
- Inspect JSON copied from logs or terminals
CI/CD Pipelines
- Gate builds on valid JSON configs
- Validate JSON fixtures before test runs
- Catch malformed payloads in mock servers
Development Tools
- API testing
- Config validation
- Test fixtures
- Schema generation prep
JSON is stricter than JavaScript object literals — keys must be double-quoted, trailing commas are forbidden, and values like 'undefined' do not exist.
If your JSON comes from a JavaScript codebase, watch out for single-quoted strings and unquoted keys — both are valid JS but invalid JSON.
Copy-pasted JSON from PDFs, emails, or chat tools sometimes contains Unicode look-alike characters for quotes that are not ASCII double quotes.
Add JSON validation to your CI pipeline for any config or fixture files tracked in version control.
Validate JSON before passing it to any schema generator — a malformed input produces meaningless or broken type output.
When receiving JSON from third-party systems, always validate before parsing to prevent unexpected runtime errors.
Frequently Asked Questions
Find answers to common questions about our tools and services.
Understanding JSON Validator
JSON validation is the process of checking whether a text document conforms to the JSON grammar defined in RFC 8259. Despite its apparent simplicity — objects, arrays, strings, numbers, booleans, and null — JSON has several strict syntactic rules that trip up even experienced developers. Keys must be double-quoted strings. Commas must not appear after the last element of an object or array. Strings must use double quotes, not single quotes. The only valid bare keywords are true, false, and null. Numbers cannot have leading zeros (except "0" itself). These constraints are enforced rigidly; any violation produces a document that is not JSON, even if it looks close.
The most frequent source of invalid JSON is human editing. When developers manually modify JSON config files, request payloads, or fixture data, they commonly introduce trailing commas after the last item (valid in JavaScript but not JSON), forget to quote a key, or use single quotes copied from a language that allows them. JSON copied from web browsers' developer tools or log aggregators sometimes includes Unicode smart quotes or em dashes that visually resemble standard ASCII punctuation but parse as invalid characters. A validator catches all of these issues immediately, before the malformed JSON reaches an application parser that might throw a cryptic internal error.
Automated validation is especially valuable in CI/CD pipelines. Many projects store JSON configuration files, Kubernetes manifests, test fixtures, or OpenAPI schema definitions in version control. A pre-commit hook or pipeline step that validates these files prevents malformed JSON from being merged and breaking builds. Running a JSON validator as part of a deployment gate is far cheaper than diagnosing a production failure caused by an invalid config file that was never checked. Most modern linting tools include JSON validation, but having a standalone online validator provides a quick manual check during development without requiring local tooling.
This JSON Validator implements the full RFC 8259 parsing rules and provides precise error feedback. When validation fails, the tool reports the nature of the error — unexpected token, invalid string escape sequence, mismatched delimiter, or trailing comma — along with contextual information to locate the problem. Validation runs entirely in the browser, ensuring that confidential JSON payloads such as API tokens, database connection strings, or private configuration values are never transmitted to external servers. Once validation passes, the validated JSON can be piped directly to the formatter or minifier tools without re-entering the data.