Syntax and schema validation
Validation tools
Secure offline syntax checking of configuration files, schemas, and markup.
Are you familiar with the situation where a project won't start or breaks after deployment due to a missing space in YAML, an extra comma in JSON, or a syntax error in Dockerfile, and you're looking for a way to quickly check the config?
Our validators are designed to quickly and confidentially validate your configuration files, markup, and databases. Because code processing is done locally in the browser, your passwords, API keys, and secrets stay completely safe.
We support HTML, XML, JSON, YAML, TOML, CSV, INI, ENV, Dockerfile, Cron and JSON Schema, detecting errors and showing the exact problem string for instant fixes.
Validators in this category
18 tools
Cron Validator
Offline syntax checking of Cron expressions with human-language interpretation of the schedule.
- Validates Cron file syntax client-side with no external overhead.
- Outputs a clear validation summary and statistics.
- Displays a code snippet pointing to the invalid token.
CSV Validator
Quickly check CSV files for integrity, delimiters and column matching offline.
- Validates CSV file syntax client-side with no external overhead.
- Outputs a clear validation summary and statistics.
- Displays a code snippet pointing to the invalid token.
Dockerfile Validator
Syntax validation and best practices for writing Dockerfiles locally in the browser.
- Validates Dockerfile file syntax client-side with no external overhead.
- Outputs a clear validation summary and statistics.
- Displays a code snippet pointing to the invalid token.
ENV Validator
Analyze .env files for syntax correctness, open quotes and duplicate keys offline.
- Validates ENV file syntax client-side with no external overhead.
- Outputs a clear validation summary and statistics.
- Displays a code snippet pointing to the invalid token.
Gitignore Tester
Paste your .gitignore rules and a list of file paths to see exactly which files are ignored, by which exact rule and line, and which negation rules are silently dead because a parent directory is already ignored.
- Reimplements git's real .gitignore matching: comments, escaped characters, trailing-space stripping, `/`-anchoring, trailing-`/` directory-only rules, `*`, `?`, `[abc]` classes and `**` across directory boundaries.
- Evaluates each path the way git actually does — directory by directory from the root — so a file inside an ignored directory is correctly reported as ignored even when a later `!` rule would otherwise seem to un-ignore it.
- The result table names the exact rule text and line number that decided each path, and flags shadowed negations with a plain-language explanation of why they have no effect.
HTML Validator
Analyze HTML code for open tags, nesting correctness and markup validity offline.
- Validates HTML file syntax client-side with no external overhead.
- Outputs a clear validation summary and statistics.
- Displays a code snippet pointing to the invalid token.
IBAN Validator
Validate an IBAN's real ISO 7064 mod-97 checksum and cross-check its total length against a bundled per-country format table — entirely offline in your browser.
- Real BigInt mod-97 checksum computation, correct for IBANs of any length up to 34 characters.
- Per-country fixed-length lookup table covering 79 countries (ISO 13616 registry), with a specific mismatch message when the length is wrong.
- Step-by-step breakdown: rearranged form, letter-to-number expansion and the exact mod-97 remainder, plus a one-click copy of the full result.
INI Validator
Validation of INI configuration files for correct sections, keys and values offline.
- Validates INI file syntax client-side with no external overhead.
- Outputs a clear validation summary and statistics.
- Displays a code snippet pointing to the invalid token.
JSON Schema Validator
Validation of JSON documents against a given JSON Schema locally.
- Validates JSON Schema file syntax client-side with no external overhead.
- Outputs a clear validation summary and statistics.
- Displays a code snippet pointing to the invalid token.
JSON Validator
Check JSON structure and configurations for errors offline in the browser.
- Validates JSON file syntax client-side with no external overhead.
- Outputs a clear validation summary and statistics.
- Displays a code snippet pointing to the invalid token.
Kubernetes Manifest Linter
Lint Kubernetes YAML manifests against cluster-hardening best practices, entirely offline in your browser.
- Hand-rolled YAML parser — no external library, so nothing is sent anywhere to be parsed.
- Rule table modeled on the CIS Kubernetes Benchmark, kube-score, and Pod Security Standards guidance.
- Understands Pod, Deployment, StatefulSet, DaemonSet, Job, ReplicaSet, and CronJob manifests.
Robots.txt Tester
Paste a robots.txt file, pick a crawler — including GPTBot, ClaudeBot and Google-Extended — and instantly see whether it can fetch a given URL path, with the exact rule and line number that decided it.
- Reimplements the actual robots.txt algorithm (Google's REP / RFC 9309): case-insensitive user-agent groups, ordered Allow/Disallow rules, `*` and `$` wildcards in paths.
- Picks the most specific matching user-agent group for the crawler you choose — an exact/prefix product-token match always beats the `*` fallback group.
- Shows exactly which line decided the verdict, e.g. "Blocked because of line 4: `Disallow: /admin`", plus a reference table explaining what each bundled crawler token is.
Sitemap.xml Validator — Real Protocol Compliance Checker
Paste or upload a sitemap.xml (or sitemap index) and validate it against the real sitemaps.org protocol: root element and namespace, absolute <loc> URLs, the documented 50,000-URL / 50MB limits, <lastmod>, <priority>, <changefreq> — plus a freshness histogram and duplicate-URL detection.
- Genuine per-rule pass/fail report — root element & namespace, URL count & file-size limits, <loc> validity, <lastmod>/<priority>/<changefreq> — each with real counts and up to 50 specific offending entries listed, plus a "+N more" note beyond that.
- Automatically detects whether the file is a sitemap (<urlset>) or a sitemap index (<sitemapindex>) and adjusts the checks accordingly — <priority> and <changefreq> only apply to <urlset> entries.
- Paste XML directly or drag-and-drop/upload a .xml file, read locally via the File API and never uploaded anywhere.
TOML Validator
Check the syntax and structure of TOML configuration files locally and securely.
- Validates TOML file syntax client-side with no external overhead.
- Outputs a clear validation summary and statistics.
- Displays a code snippet pointing to the invalid token.
TSV Validator
Validate TSV (Tab Separated Value) files for integrity and structure offline.
- Validates TSV file syntax client-side with no external overhead.
- Outputs a clear validation summary and statistics.
- Displays a code snippet pointing to the invalid token.
Web App Manifest Validator
Validate a PWA manifest.json against the Web App Manifest spec and preview maskable icons against Android's adaptive-icon safe zone.
- Plain-English errors and warnings for every field the W3C Web App Manifest spec requires or recommends.
- Per-icon safe-zone geometry check: real pixel analysis flags artwork or transparency outside the adaptive-icon safe circle.
- Matches uploaded icon files to the manifest's icons[].src entries by filename to render actual home-screen previews.
XML Validator
Validate XML code and configuration files for syntax and closed tags offline.
- Validates XML file syntax client-side with no external overhead.
- Outputs a clear validation summary and statistics.
- Displays a code snippet pointing to the invalid token.
YAML Validator
Check YAML configurations (Kubernetes, CI/CD) for correct indentation offline.
- Validates YAML file syntax client-side with no external overhead.
- Outputs a clear validation summary and statistics.
- Displays a code snippet pointing to the invalid token.