Data & format validators
104 free browser-based validators and checkers for data formats, APIs, markup, configs, and more. Line-aware errors, no signup.
Data formats
Data format validation for JSON, CSV, XML, and YAML—syntax, structure, and quality signals with line-aware errors and links to deeper guides on ValidateThis.
JSON & schema(6)
JSON ValidatorValidate JSON syntax with precise error locations. Check for trailing commas, missing quotes, and malformed structures.JSON FormatterPretty-print or minify JSON with optional jsonrepair.JSON Schema ValidatorPaste JSON Schema + instance; validate with Ajv in the browser.JSONL ValidatorJSON Lines / NDJSON: non-empty lines must parse as JSON; flags blank lines.AI JSON Output ValidatorValidate that text parses as JSON (with optional repair).Data Format AnalyzerPaste JSON to validate syntax, structure, size. Get validation score and fix recommendations.
CSV, tables & SQL(5)
CSV ValidatorValidate CSV structure, RFC 4180 quoting, and consistent column count per row.CSV to JSONConvert CSV rows to JSON objects or arrays.Data Quality AnalyzerPaste JSON to check missing values, duplicate rows, and data quality. Get a quality score.Duplicate Line CheckerFind repeated lines and line numbers.SQL SELECT Syntax CheckerHeuristic read-only checks for SELECT/WITH: keywords, parens, single statement.
XML & YAML(2)
IDs, URLs & checksums(10)
URL ValidatorQuick http(s) URL string format check.IP Address ValidatorIPv4 / IPv6 format pattern check.Credit Card Validator (Luhn)Luhn checksum on card number digits (education / QA only).IBAN ValidatorIBAN structure and mod-97 check digits.SWIFT/BIC ValidatorSWIFT/BIC 8 or 11 character format check.IMEI Luhn Validator15-digit IMEI with Luhn checksum — format only.ISBN-10/13 Checksum ValidatorISBN-10 (X allowed) or ISBN-13 check digit verification.EAN-13 Barcode ValidatorGTIN-13 / EAN-13 mod-10 check digit on 13 digits.Relative URL ResolverJoin base URL + relative reference with the URL constructor.URL Path Segment Safe CheckStrict path segment / percent-encoding character lint.
Geo, contacts & certificates(9)
GeoJSON LintJSON parse plus GeoJSON type and FeatureCollection structure hints.WKT Geometry LintWell-Known Text keyword and parenthesis balance check.PostGIS EWKT Prefix CheckOptional SRID=n; plus WKT keyword and balanced parentheses.iCalendar (.ics) ValidatorBEGIN/END stack lint for iCalendar with VCALENDAR hints.vCard ValidatorShallow vCard check: VCARD wrappers, FN, and VERSION hints.X.509 PEM Certificate ViewerView subject, issuer, validity, SHA-256 fingerprint, SAN from PEM certs in the browser.ASN.1 OID Format CheckDotted-decimal OID string rules (arcs, ITU first-arc constraints).Raw Email Headers LintUnfold folded headers and flag missing colons, empty values, and duplicates.MIME Multipart Tree ViewerParse boundary-delimited multipart body: top-level parts and byte sizes.
Text, encoding & AI helpers(4)
UTF-8 Text ValidatorUTF-8 byte length and round-trip sanity check.Unicode Normalization CheckerCompare two strings under NFC, NFD, NFKC, and NFKD side by side.Punycode & IDN ToolTurn an IDN hostname into ASCII (punycode) using the URL API.Token CounterCharacter/word counts and rough token estimate (chars ÷ 4) for prompts. Not tiktoken.
API & responses
API response body checks, SOAP envelopes, webhook payloads, HMAC signatures, and replay windows—quick triage before you ship integrations or debug production traffic.
Response & webhook bodies(3)
API Response CheckerValidate API response body as JSON. Paste raw HTTP response or JSON only; get line/column errors.Webhook Payload ValidatorValidate webhook payload: valid JSON and optional required top-level keys.OpenAI Response Format CheckerHeuristics for OpenAI-style JSON envelopes (choices, error).
Auth, signatures & replay(3)
HTTP mechanics(6)
CORS Preflight CheckerReview OPTIONS CORS headers against Origin and method — Allow-Origin, credentials, methods.HTTP Response Headers LintHeuristic lint for pasted response headers: caching, HSTS, MIME hints, duplicates.HTTP Link Header ParserParse Link header values: URLs in angle brackets and rel/type/title parameters.ETag Format ValidatorValidate weak/strong ETag tokens and comma-separated If-None-Match style lists.Content-Type vs Body SniffCompare declared MIME type to a simple first-bytes sniff of JSON, HTML, XML, or YAML.Multipart Boundary CheckerConfirm multipart boundary= matches dash delimiters in the raw body.
Markup & structure
HTML and CSS syntax, RSS/Atom feeds, Schema.org JSON-LD, and structural analyzers for documents you publish to the web or feed into parsers.
HTML, CSS & accessibility(4)
HTML ValidatorCheck HTML markup for syntax errors, unclosed tags, invalid nesting, and W3C compliance issues.CSS ValidatorValidate CSS stylesheet syntax (PostCSS parse). Line/column errors for malformed rules — grammar focus, not browser support.HTML Entities Round-TripBrowser encode/decode round-trip for pasted text snippets.WCAG Contrast CheckerContrast ratio from two hex colors (sRGB luminance).
Feeds & Schema.org(2)
Markdown, XSD & structure(3)
Markdown ValidatorLightweight Markdown heuristics (fences, headings).XSD Schema CheckerValidate XML against an XSD schema. Paste XSD and XML; get line and column errors when the document does not conform.Config Structure CheckerValidate JSON or YAML config: syntax and optional required top-level keys. Paste config, list required keys.
Config & env
CI/CD YAML (GitHub Actions, GitLab CI), .env files, secrets scanning, and configuration structure checks to catch mistakes before deploy.
Env files & secrets(2)
Infra configs(5)
Docker Compose Structure LintYAML-parse compose files and check services object shape and top-level keys.Kubernetes Manifest Quick LintYAML-parse K8s objects: apiVersion, kind, metadata hints for single docs or lists.nginx.conf Bracket LintBrace balance for nginx configs with # comments and quotes skipped heuristically.Apache .htaccess LintMatch IfModule/Directory-style section open/close tags on trimmed lines.Content-Security-Policy AnalyzerBreak down CSP directives and flag common weak sources (unsafe-inline, unsafe-eval, frame-ancestors *).
App manifests & lockfiles(6)
TOML ValidatorParse TOML for syntax errors in the browser (configs, manifests).INI & Properties LintLint INI sections and Java .properties: keys, duplicates, continuation lines.EditorConfig CheckerValidate .editorconfig sections and standard indent/EOL/charset keys.package.json ConsistencyShallow package.json lint: JSON shape, engines, dependency value types, and common fields.Lockfile Change SummarizerCompare two npm lockfile JSON pastes: package entry counts (v2) or dependencies (v1).Semver Range InterpreterInterpret caret/tilde/npm ranges: valid range, min version, sample satisfies, and sample max.
Regex & patterns
Regular expressions, glob patterns, and match debuggers—test patterns safely, inspect captures, and validate strings used in routing, logs, and automation.
Regex TesterTest regular expressions against text. See matches, capture groups, and flags (g, i, m, s).Pattern ValidatorValidate glob patterns and test paths. See which paths match (e.g. src/**/*.ts, *.json).Match DebuggerDebug regex matches: see start index, end index, length, and matched text for each match.
Logs & errors
Log analysis, error-pattern search, and log-line format validation—ideal for on-call triage, noisy pipelines, and structured logging QA.
Log triage(3)
Log File AnalyzerAnalyze log files: count lines by level (ERROR, WARN, INFO, DEBUG, TRACE) and see sample lines.Error Pattern CheckerFind log lines that match a pattern: plain text or regex. Get matching lines with line numbers.Log Format ValidatorValidate that each log line matches an expected format (regex). Paste logs, enter pattern, get invalid lines.
Diff & patch(3)
Encoding & hashing
Base64, checksums, and cryptographic hash format checks—verify integrity of payloads, configs, and artifacts without leaving the browser when possible.
Checksums & hashes(2)
Date, time & IDs
Date/time parsing, ISO and RFC formats, Unix timestamps, UUID generation and validation, and ID collision checks for distributed systems.
Dates, timestamps & cron(4)
Date-Time Format ValidatorValidate date-time strings (ISO 8601, RFC 2822). Get parsed result in ISO format.ISO Compliance CheckerCheck if a date-time string is strictly ISO 8601 compliant. Get violations and parsed result.Timestamp ConverterConvert Unix timestamp (seconds or ms) to ISO date-time and vice versa.Cron Expression ExplainerHuman summary plus next run times from a cron expression (cron-parser + cRonstrue).
UUIDs & IDs(2)
SEO & crawlers
robots.txt rules, XML sitemaps, meta and Open Graph tags, Twitter cards, canonical URLs, and hreflang extraction for crawler-facing markup review.
robots.txt, sitemaps & AI crawlers(4)
robots.txt TesterTest robots.txt rules against URLs to verify crawler access permissions and sitemap declarations.Sitemap.xml ValidatorParse sitemap XML and list loc URLs (urlset or index).robots.txt vs Meta Robots CompareCompare robots.txt allow/disallow for a path with meta robots noindex/none signals.llms.txt Structure ValidatorHeuristic checks for title, sections, and URL lines in llms.txt.