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Syntax and schema validation

Validation tools

Secure offline syntax checking of configuration files, schemas, and markup.

Validators check one format each: JSON, YAML, HTML, XML, TOML, CSV, INI, ENV, a Dockerfile, cron, or a JSON Schema. They report the line that failed.

Use one when a project will not start because of a stray comma or a bad indent, and you want the check to happen in this tab rather than on a pastebin.

A validator says whether the syntax parses. It does not say whether the config is the right one for your server, and a secret in the file stays in this browser only for as long as the tab is open.

Validators in this category

12 tools

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Cron Validator

Offline syntax checking of Cron expressions with human-language interpretation of the schedule.

Use this tool when Do you need to set up a daily database backup at 3 am and check the correctness of the cron string?

  • 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.
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CSV Validator

Check that every non-empty CSV row has the same number of comma-separated fields as the first row.

Use this tool when Do you need to check a CSV file exported from Excel before uploading it to your site?

  • Separator is the comma
  • A trailing empty line is ignored
  • An unclosed quote fails on that line
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Dockerfile Validator

Check a Dockerfile for an uppercase instruction, a FROM line, and a small set of argument shapes.

Use this tool when Do you need to check your Dockerfile for errors before committing your code to the repository?

  • Backslash continuations are joined before the check
  • Unknown instruction names fail
  • No build is run and no image is pulled
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ENV Validator

Check a .env file for KEY=VALUE rows, duplicate keys, and quotes that open and do not close.

Use this tool when Need to securely check your .env file with passwords before deploying your project?

  • Blank lines and # comments are skipped
  • Keys are case-insensitive in the pattern, so lowercase is allowed
  • The word export in front of a key is not stripped
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HTML Validator

Check that HTML tags nest and close, and that quotes inside a tag are finished.

Use this tool when Do you need to quickly find the cause of a broken layout on a page?

  • Matches opening and closing tag names
  • Flags an unclosed quote inside a tag
  • Lets img, br, and the other void tags omit a closer
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INI Validator

Check INI text for sections, key=value lines, comments, and duplicate names. It does not look for HTML tags.

Use this tool when Do you need to check the correctness of the php.ini file or other server configs?

  • Empty section names are rejected
  • A line that is not a section or a key=value row fails
  • Values are not type-checked
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JSON Schema Validator

Check one JSON value against a small subset of JSON Schema: types, ranges, required keys, properties, items, pattern, and enum.

Use this tool when Need to test your API response against the OpenAPI specification?

  • Types string, number, integer, boolean, object, array, and null
  • properties and items applied one level at a time
  • Extra keys are allowed, because additionalProperties is not read
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JSON Validator

Check JSON structure and configurations for errors offline in the browser.

Use this tool when Fix syntax errors in application configurations before deployment.

  • 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.
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TOML Validator

Check TOML-like lines for section headers, key = value pairs, duplicates, and simple quotes and brackets.

Use this tool when Do you need to check the configuration file Cargo.toml or pyproject.toml before committing?

  • Comments are whole lines starting with # or ;
  • Keys must match a limited character set
  • No multiline values and no dotted-key nesting
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TSV Validator

Check that every non-empty TSV row has the same number of tab-separated fields as the first row.

Use this tool when Do you need to check the structure of a large TSV file before uploading it to the database?

  • Separator is the tab character
  • A trailing empty line is ignored
  • An unclosed quote fails on that line
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XML Validator

Check that XML is well-formed: prolog version, matched tags, and closed quotes.

Use this tool when Do you need to test an XML feed for an online store before publishing it?

  • Well-formedness only: matched tags and closed quotes
  • A prolog must include version when a prolog is present
  • CDATA is skipped so text inside it is not read as tags
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YAML Validator

Check YAML-like lines for indentation, keys, duplicates, and quotes. This is not a full YAML 1.2 parser.

Use this tool when Need to verify your Kubernetes configuration before deploying?

  • Keys limited to a fixed character set
  • Unclosed quotes on a single-line value fail
  • No anchors, tags, or flow collections

More tools

The rest of the catalogue. Each tool still runs in your browser.