Inline Styles Over Stylesheets
Put critical styling inline on each element. External stylesheets barely work in email, and
About Email HTML Validator
Email HTML Validator runs your markup through a set of email-specific checks that go far beyond basic tag validation. Paste your HTML and get a scored compatibility report covering tag structure, unsupported elements, images, links, inline styling, table layout, and total message size — each issue with a line number so you can fix it fast.
Email clients are notoriously inconsistent about what HTML they support. This tool encodes the rules that matter most for Gmail, Outlook, Apple Mail, and mobile clients, helping you catch rendering-breaking problems before you hit send.
Features
- Tag structure analysis: Balance and nesting checks report mismatched, unclosed, and orphaned tags with line numbers.
- Client support linting: Flags scripts, forms, iframes, media tags, and semantic elements that break or render inconsistently in email clients.
- Image checks: Verifies alt text, explicit dimensions, and absolute https image URLs.
- Link checks: Detects missing hrefs, relative URLs, and blocked javascript: links.
- Inline CSS and table guidance: Reminds you where external styles and semantic blocks will cause trouble.
- Scored report: A 0-100 compatibility score with error, warning, and info counts you can filter.
- Size analysis: Measures the raw HTML size against the ~100 KB email limit.
How to Use
- Paste your email HTML into the editor, or click Load Sample to try a well-formed table-based email.
- Click Validate HTML to run the full set of checks.
- Review the score and counts — errors first, then warnings and info.
- Use the line numbers to jump into your markup and fix each flagged issue.
- Re-validate until you reach a clean report, then test in real clients.
Examples
Example 1: A table-based newsletter with a doctype, meta charset, role="presentation" tables, inline styles, alt text on every image, and absolute https links validates with a high score and no errors.
Example 2: A template with a script tag, a div-based layout, an ![]()
without alt or width, and a relative image URL produces errors and warnings across the support, images, and style categories, all shown with line numbers.
Benefits
- Catch breakage early: Find rendering-breaking issues before a campaign goes out.
- Faster fixes: Line numbers point straight to the problem in your markup.
- Client-aware rules: Checks are specific to email client quirks, not generic web validation.
- Deliverability support: Clean HTML and safe size limits help protect sender reputation.
- 100% free and private: No sign-up, no upload, everything runs locally in your browser.
Frequently Asked Questions
What does this validator check?
It checks tag balance and nesting, unsupported tags for email clients, image alt text and absolute https URLs, link integrity, table layout conventions, inline vs external CSS, and total message size — then produces a scored report with line numbers.
Why does my HTML render differently in email clients?
Email clients do not use a single web engine. Gmail, Outlook, and Apple Mail each support different subsets of HTML and CSS, and most strip scripts, forms, and external stylesheets. Designing with tables and inline styles is the most reliable approach.
Do I need to use tables for email layout?
Not always, but tables remain the most compatible layout method across all major clients. Modern clients handle flexbox better than they used to, yet Outlook desktop still requires table-based, width-constrained layout to render predictably.
Why do my images not load in some clients?
Images commonly fail when the src is relative, when the URL uses http instead of https, or when the image host is blocked. Always use absolute https URLs, add alt text, and set explicit width and height.
Is inline CSS required in email?
Inline styles are the most reliable across clients. <style> blocks in the head are supported by many clients now but are still inconsistent, and external stylesheets are essentially unsupported, so prefer inline styles for critical styling.
What is the email size limit?
Most providers recommend keeping the raw HTML under roughly 100 KB. Above that, some clients truncate messages or refuse to load them, and large files also hurt deliverability and load speed.
Is this tool 100% accurate?
No validator can be perfect because clients change over time. This tool applies the most common, widely documented email HTML rules and flags likely issues, but you should always test your final template in real clients.