ValidateThis

Data & format validators

107 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.

Data Format AnalyzerPaste JSON to validate syntax, structure, size. Get validation score and fix recommendations.Data Quality AnalyzerPaste JSON to check missing values, duplicate rows, and data quality. Get a quality score.JSON ValidatorValidate JSON syntax with precise error locations. Check for trailing commas, missing quotes, and malformed structures.CSV ValidatorValidate CSV structure, RFC 4180 quoting, and consistent column count per row.XML ValidatorValidate well-formed XML. Check unclosed tags, invalid attributes, syntax. Line and column errors.YAML ValidatorValidate YAML syntax. Check indentation, structure. Get line and column errors.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.JSON FormatterPretty-print or minify JSON with optional jsonrepair.UTF-8 Text ValidatorUTF-8 byte length and round-trip sanity check.CSV to JSONConvert CSV rows to JSON objects or arrays.Duplicate Line CheckerFind repeated lines and line numbers.Prompt ValidatorCharacter/word counts and rough token estimate for prompts.AI JSON Output ValidatorValidate that text parses as JSON (with optional repair).Token CounterRough token estimate (chars ÷ 4) plus word count.X.509 PEM Certificate ViewerView subject, issuer, validity, SHA-256 fingerprint, SAN from PEM certs in the browser.NDJSON ValidatorValidate newline-delimited JSON: one JSON object/array per line, line-numbered errors.JSONL ValidatorJSON Lines format: non-empty lines must parse as JSON; flags blank lines.JSON Schema ValidatorPaste JSON Schema + instance; validate with Ajv in the browser.SQL SELECT Syntax CheckerHeuristic read-only checks for SELECT/WITH: keywords, parens, single statement.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.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.iCalendar (.ics) ValidatorBEGIN/END stack lint for iCalendar with VCALENDAR hints.vCard ValidatorShallow vCard check: VCARD wrappers, FN, and VERSION hints.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.ASN.1 OID Format CheckDotted-decimal OID string rules (arcs, ITU first-arc constraints).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.

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.

API Response CheckerValidate API response body as JSON. Paste raw HTTP response or JSON only; get line/column errors.SOAP Response ValidatorValidate SOAP response: well-formed XML and valid Envelope with Body or Fault. Paste raw HTTP or SOAP XML.Webhook Payload ValidatorValidate webhook payload: valid JSON and optional required top-level keys.Signature CheckerVerify HMAC signature (SHA-256 or SHA-1) of a payload against a secret.Replay TesterCheck if a timestamp is within an allowed time window (replay protection).OpenAI Response Format CheckerHeuristics for OpenAI-style JSON envelopes (choices, error).JWT Claims InspectorDecode JWT header and payload (JWS). exp/nbf hints. Signature not verified.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.OpenAPI Snippet LintStructural checks on OpenAPI 3 or Swagger 2 YAML/JSON fragments.GraphQL Query Syntax LintParse GraphQL queries or SDL with the official graphql parser.

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 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.RSS / Atom Feed ValidatorValidate RSS 2.0 or Atom XML: well-formed XML plus core channel/feed structure.Schema.org ValidatorValidate JSON-LD, Microdata, and RDFa structured data for SEO and rich search results.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.Markdown ValidatorLightweight Markdown heuristics (fences, headings).WCAG Contrast CheckerContrast ratio from two hex colors (sRGB luminance).HTML Entities Round-TripBrowser encode/decode round-trip for pasted text snippets.

Config & env

CI/CD YAML (GitHub Actions, GitLab CI), .env files, secrets scanning, and configuration structure checks to catch mistakes before deploy.

CI Config LinterLint CI config YAML: GitHub Actions and GitLab CI. Validate syntax and structure (on, jobs, steps, runs-on, script).Env File ValidatorValidate .env file syntax: KEY=value, comments (#), duplicate keys, invalid key names..env Syntax CheckerCheck .env file line syntax: KEY=value, comments (#), invalid key names. Same API as Env File Validator.Secrets ScannerScan text for potential secrets: passwords, API keys, tokens. Get line numbers and pattern names.Content-Security-Policy AnalyzerBreak down CSP directives and flag common weak sources (unsafe-inline, unsafe-eval, frame-ancestors *).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.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.Semver Range InterpreterInterpret caret/tilde/npm ranges: valid range, min version, sample satisfies, and sample max.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).

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 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.Git Diff Hunk ParserParse unified diff: list +++ paths and count @@ hunks per file.Unified Diff ValidatorValidate unified diff @@ lines and file headers before hunks.Git Apply Patch CheckerLint patch text for ---/+++ and @@ structure with per-file hints.ANSI Escape CleanerRemove CSI/OSC and common ANSI codes from pasted log or terminal output.

Encoding & hashing

Base64, checksums, and cryptographic hash format checks—verify integrity of payloads, configs, and artifacts without leaving the browser when possible.

Base64 Encoder / DecoderEncode text to Base64 and decode Base64 to text. Paste input, choose mode, get the result.Checksum CheckerCompute MD5, SHA-1, or SHA-256 checksum of text. Optionally verify against an expected hash.Hash ValidatorValidate that a string is a valid hash format (hex length for MD5, SHA-1, SHA-256, etc.). Auto-detect or specify algorithm.Hex String & Byte Length CheckValidate hex nibbles and count bytes after stripping 0x and spaces.

Date, time & IDs

Date/time parsing, ISO and RFC formats, Unix timestamps, UUID generation and validation, and ID collision checks for distributed systems.

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.UUID Generator & ValidatorGenerate UUID v4 and validate UUID format (version and variant).ID Collision CheckerPaste a list of IDs (one per line); find duplicates and line numbers.Format CheckerValidate a string against named formats: email, URL, IPv4, UUID, semver, etc.Cron Expression ExplainerHuman summary plus next run times from a cron expression (cron-parser + cRonstrue).

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 TesterTest robots.txt rules against URLs to verify crawler access permissions and sitemap declarations.Meta Tags ValidatorExtract title and meta tags from pasted HTML or a fetched page.Open Graph ValidatorList og:* Open Graph meta tags from HTML head.Twitter Card ValidatorList twitter:* meta tags from HTML head.Canonical URL CheckerFind rel=canonical link in document head.Hreflang ValidatorList hreflang alternate links from HTML head.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.