Markdown Validator & Linter
Validate and lint your Markdown files online for free. Our linter checks heading structure, link syntax, image alt text, code block formatting, list consistency, table column alignment, emphasis markers, reference links, HTML usage, and common formatting issues with detailed error messages and line numbers. Perfect for README files, documentation, blog posts, and technical writing.
Paste your Markdown content to check for heading structure, link syntax, image alt text, code block issues, list formatting, table column alignment, emphasis markers, HTML usage, trailing whitespace, and best-practice violations.
Why Use Our Markdown Validator?
Instant Validation
Our tool to validate Markdown analyzes your content instantly in your browser. Validate Markdown files of any size with zero wait time — get detailed error reports with line numbers in milliseconds.
Secure & Private Processing
Your data never leaves your browser when you use our Markdown lint online tool. Everything is processed locally using JavaScript, ensuring complete privacy and security for sensitive configuration data.
No File Size Limits
Validate large Markdown files without restrictions. Our free Markdown Validator handles any size input — from small configs to massive files with thousands of entries.
100% Free Forever
Use our Markdown Validator completely free with no limitations. No signup required, no hidden fees, no premium tiers, no ads — just unlimited, free validation whenever you need it. The best free Markdown lint online available.
Common Use Cases for Markdown Validator
Heading Structure Validation
Validate heading hierarchy for correct document outline. Detect missing H1, multiple H1 headings, skipped heading levels (H2 to H4), empty headings, missing spaces after # markers, and inconsistent heading styles (ATX vs Setext).
Link & Image Checking
Validate inline links, reference links, and images for correct syntax. Detect empty URLs, missing alt text, bare URLs without formatting, spaces in URLs, undefined reference links, and empty link display text for accessibility.
Code Block Validation
Check fenced code blocks for unclosed fences, missing language identifiers, and proper formatting. Detect mismatched backtick/tilde fences and recommend language hints for syntax highlighting support.
List & Task List Formatting
Validate unordered list marker consistency (-, *, +), ordered list starting numbers, nested list indentation, and task list checkbox syntax. Detect inconsistent markers across the document and odd indentation levels.
Table Structure Checks
Validate table formatting with column count consistency between header, separator, and body rows. Detect mismatched column counts across rows ensuring tables render correctly in all Markdown processors.
Style & Best Practices
Detect trailing whitespace, consecutive blank lines, tab characters, raw HTML usage, unmatched emphasis markers (** and __), long lines, inconsistent horizontal rules, bare URLs, and missing trailing newlines.
Understanding Markdown Validation
What is Markdown Validation?
Markdown validation is the process of checking Markdown (.md) files (.md) for syntax errors, structural issues, invalid values, duplicate keys, and specification compliance — helping you catch problems before deployment. Markdown is widely used for writing structured documents with headings, lists, links, images, code blocks, tables, blockquotes, emphasis, horizontal rules, task lists, and reference links using lightweight plain-text formatting syntax. Our free Markdown lint online tool checks your content instantly in your browser. Whether you need to validate Markdown for README files, documentation, blog posts, wikis, technical writing, API documentation, release notes, changelogs, knowledge bases, tutorials, and static site content, our tool finds errors accurately and privately.
How Our Markdown validator Works
- Input Your Markdown Content: Paste your Markdown content directly into the text area or upload a
.mdfile from your device. Our Markdown lint online tool accepts any Markdown input. - Instant Browser-Based Validation: Click the "Validate Markdown" button. Our tool analyzes your content entirely in your browser — no data is sent to any server, ensuring complete privacy.
- Review Detailed Error Reports: View a comprehensive list of errors with line numbers, descriptions, and severity levels. Fix issues with pinpoint accuracy using our clear error messages.
What Gets Validated
- Syntax Correctness: Checks for proper syntax including balanced brackets, correct string quoting, valid escape sequences, and proper key-value pair formatting.
- Data Types: Validates integers, floats, booleans, strings, datetimes, arrays, and inline tables conform to the Markdown specification.
- Structural Integrity: Detects duplicate keys, conflicting table definitions, invalid table headers, and malformed sections.
- Line-by-Line Reporting: Every error includes its exact line number and a clear description, making it easy to find and fix issues in your Markdown files.
Related Tools
JSON to YAML
Convert JSON to YAML format instantly - Free online JSON to YAML converter
XML to YAML
Convert XML to YAML format for configuration migration - Free online XML to YAML converter
CSV to YAML
Convert CSV spreadsheet data to YAML format - Free online CSV to YAML converter
TSV to YAML
Convert TSV tab-separated data to YAML format - Free online TSV to YAML converter
Frequently Asked Questions - Markdown validator
A Markdown validator is a tool that checks Markdown files for syntax errors, structural issues, invalid values, and specification compliance. Our Markdown lint online tool processes everything in your browser — giving you instant error reports with line numbers and clear descriptions.
Our Markdown validator detects syntax errors (missing brackets, incorrect quoting), structural issues (duplicate keys, conflicting table definitions), invalid data types (malformed numbers, dates, strings), invalid escape sequences, and specification violations. Each error includes its exact line number for easy debugging.
Absolutely! Your data is completely secure. All validation happens directly in your browser using JavaScript — no data is ever uploaded to any server. Your configuration files, secrets, and sensitive data never leave your device.
Yes, our Markdown validator is 100% free with absolutely no hidden costs or limitations. There's no signup required, no premium tier, no usage limits, no file size restrictions, and no advertisements. Use it unlimited times for any project.
Yes! Our Markdown lint online tool handles files of any size. Since all processing happens in your browser, performance depends on your device, but modern browsers handle even very large Markdown files efficiently.
Our validator checks for heading hierarchy issues (missing H1, skipped levels, empty headings, closed ATX style), link problems (empty URLs, missing alt text, bare URLs, undefined references), code block issues (unclosed fences, missing language hints), list formatting (inconsistent markers, odd indentation, ordered list numbering), table column mismatches, unmatched emphasis markers, trailing whitespace, consecutive blank lines, raw HTML usage, tab characters, long lines, and missing trailing newlines.
Yes! Our validator implements many rules similar to popular Markdown linters like markdownlint. It checks heading structure (MD001-MD003), list formatting (MD004-MD007, MD029-MD030), line length (MD013), trailing whitespace (MD009), blank lines (MD012), HTML usage (MD033), emphasis style, code blocks, and more. All checks are adapted for browser-based validation.
Yes! The validator checks table column count consistency between header, separator, and body rows, ensuring all rows have matching columns. For task lists, it validates checkbox syntax [x], [ ] and detects invalid checkbox characters.