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Online Code Validators

ToolSwift provides free online validators for HTML, CSS, JavaScript, JSON, and YAML. These browser-based tools help you find common syntax, structure, and formatting-related problems before using or publishing your code.

HTML Validator

Check HTML markup for common structural problems such as unclosed tags, incorrect nesting, duplicate IDs, missing image alt attributes, and other basic markup issues.

Open HTML Validator →

CSS Validator

Review CSS for common syntax problems and mistakes that can prevent stylesheets from behaving as expected. Useful for quick checks while editing CSS.

Open CSS Validator →

JavaScript Validator

Check JavaScript code for common syntax issues before running or deploying it. Useful when testing scripts, functions, snippets, and small code changes.

Open JavaScript Validator →

JSON Validator

Validate JSON data and identify syntax errors such as malformed objects, arrays, missing separators, and invalid JSON structure.

Open JSON Validator →

YAML Validator

Check YAML documents for common syntax and indentation problems. It is useful for configuration files, application settings, and structured data.

Open YAML Validator →

What Is a Code Validator?

A code validator checks source code or structured data against rules that help identify possible errors. Validation is useful because a small syntax or structure mistake can cause unexpected results in a browser, application, configuration file, or development workflow.

Why Use Online Validators?

  • Find common mistakes before publishing or deploying code.
  • Quickly check a code snippet without installing additional software.
  • Review data and configuration files during development.
  • Make debugging easier by identifying likely syntax or structure problems.
  • Use separate validators for different languages and data formats.

How to Choose the Right Validator

Choose the validator that matches the content you are checking. Use the HTML Validator for webpage markup, CSS Validator for stylesheets, JavaScript Validator for scripts, JSON Validator for JSON data, and YAML Validator for YAML documents. Each tool focuses on the type of content it is designed to inspect.

Validator vs Formatter vs Minifier

These tools perform different jobs. A validator checks for possible errors or structural problems. A formatter changes code presentation by adding indentation and line breaks to improve readability. A minifier reduces unnecessary whitespace and formatting to make code more compact.

How to Use ToolSwift Validators

  1. Select the validator for your code or data format.
  2. Paste your source into the tool or load an available example.
  3. Run the validation check.
  4. Review the reported errors or warnings.
  5. Correct the source and validate it again.

Frequently Asked Questions

Are ToolSwift validators free?

Yes. ToolSwift provides these online validators for free use in a web browser.

Do validators automatically fix my code?

Validation tools are primarily designed to identify problems. They do not replace careful review or guarantee that every issue in a project will be detected.

Can I use these validators on mobile devices?

Yes. ToolSwift validators are browser-based and can be used on supported desktop and mobile browsers.

Should I validate code before publishing?

Running a validation check before publishing can help catch common mistakes and make debugging easier, although validation should be combined with testing and review appropriate to your project.