Pasting JavaScript object literals
JSON requires double-quoted keys and strings. Comments, single quotes, undefined, and trailing commas are valid in some JavaScript contexts but invalid in JSON.
JSON Validator | Locate Strict Syntax Errors
FormattingRuns in Your Browser (No Uploads)
Validate one strict JSON document and classify syntax failures at exact line and column positions. Detect trailing commas, missing separators, incomplete containers, invalid escapes and numbers, multiple roots, control characters, and duplicate-key risk.
What to do next
Continue with a related workflow or open the next tool that usually follows this task.
Workflow guide
Format and minify code safely before deployment
Formatting and minification should produce reviewable, reproducible artifacts, not hide syntax errors or change data tokens. This workflow classifies the source and destination first, removes secrets, runs a language-specific parser, records exact settings and byte changes, compares semantic boundaries, and verifies the candidate in the real browser, compiler, loader, schema, and test suite before replacing the original.
OpenRelated toolBase64 Encoder and Decoder | UTF-8, Base64URL, and Data URIs
Strictly encode UTF-8 and decode Base64, Base64URL, data URIs, and binary byte output locally.
OpenRelated toolCSV to JSON and JSON to CSV Converter | Local and Loss-Aware
Convert CSV and JSON locally with text-safe typing, strict structure checks, and protected spreadsheet output.
OpenRelated toolHTTP Header Parser for Request and Response Debugging
Parse bounded HTTP header blocks locally with default secret masking and protocol diagnostics.
OpenHow to Use This Tool
Paste or load the complete JSON document whose syntax you need to diagnose, keeping it within the 10,000,000-byte UTF-8 cap.
Use Live mode for immediate feedback or Manual mode to validate once after editing a large document.
Read the classified error and one-based line and column, then inspect the exact comma, colon, quote, escape, number, or closing delimiter.
If syntax is valid, resolve every duplicate-key warning because different consumers may retain different values.
Run schema and application validation separately before accepting the document into an API, configuration, or migration workflow.
When to Use This Tool
Diagnose an API syntax failure
Classify a malformed request, response, webhook, or fixture before a client fails with a generic parse exception.
Check configuration syntax before CI
Find the exact broken delimiter or escape in package.json, tsconfig.json, feature flags, and application settings before commit or deploy.
Screen an import or migration document
Reject partial copies, multiple roots, trailing log text, and duplicate-key ambiguity before importing or migrating JSON records.
Learn strict JSON boundaries
Compare strict JSON rules with JavaScript object literals while seeing the exact location and class of each mistake.
Common Mistakes
Ignoring duplicate keys
Some parsers accept duplicate object keys and keep the last value. Treat duplicate keys as a data quality problem before using the payload in tests or APIs.
Validating only the changed fragment
A small fragment can be valid while the surrounding file is broken. Validate the complete object or array that your application will actually parse.
Treating syntax validity as schema validity
Syntactically valid JSON can still violate required fields, types, ranges, or business rules. Run JSON Schema or application validation after this syntax check.
Assuming every valid number is lossless everywhere
A legal JSON number may exceed exact integer or decimal precision in a downstream JavaScript consumer. Check the receiving contract and keep identifiers or exact decimals as strings when required.
Examples
Find a trailing comma in an API fixture
A copied response fails because the last property still has a comma. The validator points to the exact line before the fixture reaches a test suite.
Input
{
"status": "ok",
"count": 3,
}Output
Invalid JSON: remove the trailing comma after "count": 3.Check a config file before deployment
Validate a package, tsconfig, or app settings file locally so unclosed braces and bad escaping are caught before CI or production parsing.
Input
{"feature":"ads","enabled":true,"paths":["/en/tools"]}Output
Valid JSON with one object, one boolean field, and one paths array.Separate valid syntax from duplicate-key risk
Duplicate names do not make this document a parser syntax failure, but the warning identifies the key and path because consumers may keep different values.
Input
{
"role": "viewer",
"role": "admin"
}Output
Valid syntax with a duplicate-key warning for $.role at line 3.Find multiple root values
Two individually valid objects placed next to each other are not one JSON document. The validator points to the second root instead of accepting partial input.
Input
{"a":1}
{"b":2}Output
Invalid JSON: multiple root values begin at line 2, column 1.Bounded strict parsing, exact diagnostics, and a clear schema boundary
Syntax validation starts with one complete JSON root and recognizes objects, arrays, strings, finite numbers, booleans, and null. It reports single-quoted names or strings, comments, trailing commas, NaN, Infinity, raw control characters, and extra roots as errors.
The parser distinguishes missing separators, incomplete containers, invalid names, strings, escapes and numbers, multiple roots, and trailing content. Diagnostics use one-based line and column positions across LF, CRLF, and CR input.
Duplicate object names are reported separately from syntax failure. The source is parseable, but consumers may keep the first value, last value, or reject it, so a successful syntax status does not clear the warning.
Validation is bounded to 10,000,000 UTF-8 input bytes and 512 nesting levels. One leading byte-order mark is accepted and ignored; deeper or larger documents need a streaming or command-line parser.
All parsing remains in the current browser. Syntax validity does not establish JSON Schema compliance, numeric precision in a downstream runtime, semantic correctness, authorization, or safety to deploy.
Frequently Asked Questions
What JSON syntax errors can this validator detect?
It classifies trailing commas, missing commas or colons, incomplete braces or brackets, unterminated strings, unquoted names, invalid escapes and numbers, comments, unescaped controls, multiple roots, and trailing content. Duplicate keys produce a warning because parsers can accept them but disagree about the retained value.
Does this tool format or beautify JSON? How is it different from a JSON Formatter?
No. This tool focuses on syntax validation only. For pretty-printing or minifying, use a JSON formatter.
What byte and nesting limits apply?
The exact input limit is 10,000,000 UTF-8 bytes and nesting is limited to 512 levels. Manual mode prevents repeated live validation while editing, but it does not raise either bound. Use a streaming or command-line parser for larger or deeper documents.
Does valid JSON satisfy my schema or API contract?
No. Syntax validation proves only that the text is one parseable JSON value. It does not verify required properties, application types, value ranges, referential integrity, or authorization rules. Apply JSON Schema or your application contract next.
Is the JSON uploaded, and may I paste sensitive data?
The input is parsed in the current browser and aggregate analytics omit its content. That technical boundary does not authorize production secrets or personal data, so redact them unless your handling policy explicitly allows this browser session.
Related workflow guides
Use these focused guides when you need a practical workflow before opening the tool.
Workflow guide
Format and minify code safely before deployment
Formatting and minification should produce reviewable, reproducible artifacts, not hide syntax errors or change data tokens. This workflow classifies the source and destination first, removes secrets, runs a language-specific parser, records exact settings and byte changes, compares semantic boundaries, and verifies the candidate in the real browser, compiler, loader, schema, and test suite before replacing the original.
Workflow guideConvert CSV to JSON for spreadsheet data cleanup
Use this workflow when a spreadsheet export needs to become API-ready JSON, a fixture, or a reviewable dataset while preserving the text that the sheet actually contains.
Workflow guideFix CSV and JSON conversion errors
Use this workflow when a spreadsheet export, API fixture, or CSV/JSON handoff fails because columns shift, headers disappear, characters look broken, or JSON will not parse.
Workflow guideFormat JSON for API debugging
Use this workflow when a compact response is hard to inspect, a fixture fails strict parsing, or a generic client error must be traced to an exact JSON location without confusing syntax with API-contract validity.
Workflow guideHow to extract values from a JSON response with JSONPath
Use this workflow when a response is valid JSON but too large to inspect manually, and you need a focused list of values for debugging, QA, or documentation. Keep the expression beside the extracted result so another person can repeat the selection against a newer response instead of relying on a one-time copy.
Workflow guideDebug API JSON faster with JSONPath expressions
Use this workflow when a bug report, test failure, or production log includes a large JSON payload and you need to isolate request IDs, statuses, pagination links, or nested error fields.
Workflow guideGenerate TypeScript types from an API JSON response
Use this workflow to turn a representative API response into a useful TypeScript starting point without pretending that one payload is the complete contract. It combines strict JSON cleanup, several array samples, explicit inference review, compilation in the target project, and runtime validation at the network boundary.
Workflow guideConvert JSON and YAML configuration files safely
Use this workflow when an API example, application config, or deployment manifest needs to move between JSON and YAML without silently changing a key or numeric value.
Related Tools
Continue with another maintained workflow
Base64 Encoder and Decoder | UTF-8, Base64URL, and Data URIs
Strictly encode UTF-8 and decode Base64, Base64URL, data URIs, and binary byte output locally.
Encoding
CSV to JSON and JSON to CSV Converter | Local and Loss-Aware
Convert CSV and JSON locally with text-safe typing, strict structure checks, and protected spreadsheet output.
Converter
HTTP Header Parser for Request and Response Debugging
Parse bounded HTTP header blocks locally with default secret masking and protocol diagnostics.
Encoding
JSON Formatter | Beautify or Minify Exact JSON Text
Beautify or minify strict JSON locally while preserving duplicate keys and number text.
Formatting
JSONPath Tester | RFC 9535 Queries and Exact Matches
Test RFC 9535 JSONPath filters, slices, and selectors against JSON in your browser.
Formatting
URL Encoder and Decoder | Exact Percent Encoding and Plus Rules
Encode or decode exact URL components, full URLs, and form values locally.
Encoding