Online JSON Validator — Check Syntax with Line Numbers
Paste JSON and get instant syntax validation with clear error messages. Runs entirely in your browser — ideal before minifying, converting or committing API fixtures.
Developer notes
• Validation runs automatically after you pause typing (debounced) — no server round-trip. • The results panel is the primary surface: Valid/Invalid hero, root type, structure stats, and primitive value-type chips. • Errors show line/column plus a short humanized hint when the motif is recognized; the raw parser message stays available. • This page focuses on syntax only — use the JSON Schema validator for schema checks, the formatter to prettify, or repair when payloads are broken.
When teams pick this route
• Gate CI fixtures or OpenAPI snippets before they land in repos. • Confirm exports from YAML/CSV/XML converters parse cleanly. • Debug truncated API responses or copy-paste accidents in support tickets. • Quick check before diffing two configs or exploring them in the tree viewer.
Worked examples
Valid API envelope
Sample input
Validation result
Trailing comma caught
Sample input
Validation result
Navigate related JSON tools
Browse the JSON tools hub for the full cluster. Prettify valid payloads with the JSON formatter, compare revisions via JSON diff, or explore structure in the JSON tree viewer. Compress for APIs with our JSON minifier, or change serialization via JSON → YAML and JSON → CSV. Need schema vs data? Use JSON Schema Validator.
JSON validator FAQ
Syntax checking without leaving your browser
Does this minify or format JSON?
No — this route validates syntax only. Use the JSON minifier to compress payloads or the JSON formatter to add indentation.
How are line numbers computed?
The parser reports the first syntax error with line and column indices aligned to your pasted text.
Is my JSON uploaded?
Never — parsing and validation stay entirely inside your browser tab.
JSON with comments or trailing commas?
Strict JSON only — comments and trailing commas are rejected, matching standard JSON.parse behaviour.
Large documents?
Very large pastes may slow low-memory devices — Chrome desktop handles multi-megabyte fixtures best.
Schema validation vs syntax?
This tool checks JSON syntax only. To validate data against a JSON Schema (Draft-07 / 2020-12), use JSON Schema Validator.
JSON Tools
Validate, format, diff and explore JSON payloads — complementary to minifiers and converters.
Explore other tool categories
Minify
Shrink code and assets for production — minify JavaScript, CSS, HTML, JSON and XML before gzip or CDN deploy.
Beautify
Make code readable with consistent indentation — beautify JavaScript, CSS, TypeScript, SCSS, LESS, Markdown, GraphQL, SQL, YAML and more in your browser.
Unminify
Expand minified or compressed code — unminify JavaScript, CSS, TypeScript, SCSS, LESS, SQL, YAML and other formats when debugging or reviewing.
Conversion
Transform data between JSON, YAML, XML and CSV locally — no server uploads.
CSS preprocessors
Compile SCSS or LESS to standard CSS in the browser — pair with beautify or minify for a full stylesheet workflow.
SVG Tools
Preview, optimize with SVGO, export Data URI, resize, beautify, convert to JSX and validate SVG — all in your browser.
DevOps & Infra
Terraform HCL format/validate/minify, Dockerfile format & lint, Docker Compose and .env validation.
CI/CD
GitHub Actions and GitLab CI — format YAML and check workflow/job structure in your browser.
Logs & observability
Line-oriented JSON/NDJSON and Nginx/Apache access logs — format, filter, validate, and CSV/TSV.
Kubernetes
Multi-doc manifests, structural validate, Ingress/Deployment starters, and Helm values formatting.
Networking / IP
CIDR, subnets, and IPv4/IPv6 helpers — in your browser.
Security & tokens
JWKS, X.509 certificates, and secrets scan — browser-local.
API & schemas
OpenAPI tools to format, validate, and lint your specs.
Encoding
Encode or decode Base64, URL components and HTML entities — client-side only.
Developer utilities
Timestamps, UUID, ULID, Nanoid, cron, passwords, regex, slugify, number bases, case, text diff, and chmod — all client-side.
Text & Markdown
Count words, build Markdown TOCs, and clean line lists — all in your browser.
AI & LLM
Token counting, pricing estimates, and context-window fit — 100% browser-local.
Serialization
Serialize and deserialize PHP data structures beside JSON workflows.