HTML Editor
Runs 100% in your browserEdit HTML with a live preview — synchronized source editor, WYSIWYG visual pane, sandboxed preview, 5 starter templates, format, minify, validate, find/replace, file import, and download. 100% in your browser.
HTML source editor
Visual HTML editor — WYSIWYG
Rendered result
Editor statistics
HTML editing, visual synchronization, preview rendering, formatting, validation, copying, and downloading run entirely on this device. The preview iframe is sandboxed — scripts are disabled by default. Enable Run scripts in preview only when you need to test JavaScript; external resources in preview may still make their own network requests.
Frequently asked questions
An online HTML editor is a browser-based workspace for writing, editing, previewing, and downloading HTML without installing a desktop application. ToolsSonic combines three synchronized panes: a line-numbered source editor for precise markup, a WYSIWYG visual pane for content formatting, and a sandboxed iframe preview that renders the result in real time. All three panes stay in sync as you type.
Yes. When Live sync is enabled, the sandboxed preview updates automatically as you type in the source editor or the visual pane. You can also disable Live sync and click Refresh preview to apply the current source manually — useful when working on large documents where constant re-rendering is distracting.
WYSIWYG stands for "What You See Is What You Get." The visual editor pane in ToolsSonic lets you format content — headings, paragraphs, bold, italic, underline, lists, blockquotes, code blocks, and links — using toolbar buttons, and the formatted HTML is written back to the source editor automatically. This is useful for non-developers who prefer working with readable text rather than raw markup.
Source edits parse the HTML into the visual pane and update the sandboxed preview. Visual edits generate HTML back into the source textarea, preserving the full document shell (doctype, head, styles) when a complete document is present. A synchronization guard prevents feedback loops, and the status labels on each pane show which side generated the most recent HTML.
Yes. The preview iframe renders a full HTML document including inline styles, linked stylesheets, and scripts. Scripts are disabled by default for safety — enable Run scripts in preview only when you intentionally need to test JavaScript behavior. External resources loaded by the preview (fonts, images, scripts from CDNs) may make their own network requests even when the ToolsSonic editor itself does not.
The Validate action performs local structural checks: missing <!doctype html> declaration, unmatched closing tags, unclosed opening tags, images missing alt attributes, inline event handlers (onclick, onload, etc.), and forms with no visible form controls. Results are shown as a diagnostics panel with counts and descriptions. This is a helpful structural review — it is not a replacement for the official W3C Nu HTML Checker, browser devtools, or an accessibility audit.
Yes. Format HTML re-indents the markup with two-space indentation, collapses whitespace between tags, and produces readable multi-line output. Minify removes HTML comments and collapses whitespace around tags to produce a compact single-line payload for deployment. Neither operation uploads your HTML — both transformations run locally using JavaScript string processing.
Five starter templates are included: Starter document (a complete HTML5 document with inline styles, viewport meta, and content), Semantic article (header, section, and article elements), Responsive card (a styled card component with CSS), Accessible form (labelled inputs and a submit button), and Data table (a styled table with caption, thead, and tbody). Each template loads the relevant HTML into the source and visual panes instantly.
Yes. Click Open HTML file to read a local .html, .htm, or .txt file using the browser FileReader API — the file is read on your device and loaded into the editor without any upload. Click Download .html to save the current source as toolssonic-page.html. Both operations are entirely local.
Yes. The Find field counts case-insensitive matches in the current HTML source and updates the count as you type. Replace next substitutes the first match with the replacement text and advances focus to the substituted position in the source editor. Repeat Replace next to work through all matches one at a time.
Yes. Source editing, visual synchronization, preview rendering, format and minify transformations, validation diagnostics, copy, and download all run locally in your browser. The tool contains no network request code — no fetch, XHR, beacon, or upload. Your HTML source is not transmitted to any server, stored in localStorage, or logged. The only exception is preview content itself: if you enable scripts and your HTML references external resources, those external requests are made by the preview iframe, not by ToolsSonic.
HTML5-Editor.net and HTMLCodeEditor.com both use cookies, anonymous analytics, and targeted advertising — they are not truly private tools. ToolsSonic contains no analytics, no advertising, no cookies, and no localStorage for editor content. ToolsSonic also adds a Validate button with structural diagnostics, explicit security warnings about preview scripts, and a scripts-disabled-by-default sandbox — features not observed on those competitors. The blue hero and consistent design system match the rest of the ToolsSonic developer toolbox.
The preview uses an HTML iframe with the sandbox attribute. Without scripts enabled, the sandbox prevents JavaScript execution, form submission, navigation, and plugin content. The srcdoc attribute is used instead of src — the HTML is passed directly as a string to the iframe without creating a URL, so there is no file system access and no cross-origin request. Enabling Run scripts in preview adds the allow-scripts permission, which allows JavaScript to run in the preview while still blocking navigation and cross-origin access.
The source pane shows a synchronized line number gutter on the left — a column of numbers that scrolls with the textarea. Line numbers make it easier to locate specific elements when the Validate action reports an issue, when Find shows a match count, or when you are reviewing a long document structure. The gutter is display-only and does not affect the HTML content.
Yes. The editor maintains an in-memory history of up to 40 source states. Changes are debounced at 250ms so rapid typing creates one history entry rather than one per keystroke. History is session-only — it is cleared when you close or reload the tab and is never written to localStorage or any other persistent storage.
Yes. The three-pane layout stacks vertically on screens narrower than 900px, and each pane remains fully functional on a mobile browser. The View selector lets you switch to a single-pane mode (source, visual, or preview only) for a cleaner mobile experience. All buttons and selects are sized for touch targets.
What is HTML Editor?
An online HTML editor is a browser-based workspace for writing HTML source code, editing content visually, and rendering the result in a live preview — all without installing a software application. ToolsSonic's HTML Editor combines three synchronized panes in a single tool: a line-numbered source textarea, a WYSIWYG visual editor, and a sandboxed iframe preview.
The source pane accepts raw HTML markup with a scrollable line-number gutter. The visual pane renders the document body as editable rich text with formatting controls for headings (H1–H3), paragraphs, bold, italic, underline, strikethrough, blockquote, code block, bulleted lists, numbered lists, and hyperlink insertion. Any change in the source updates the visual pane and preview; any change in the visual pane writes clean HTML back to the source — a bidirectional sync loop that is carefully guarded against circular updates.
The preview iframe uses the HTML sandbox attribute with scripts disabled by default, and renders via the srcdoc property rather than a URL, ensuring the page content never leaves the browser tab. Users can explicitly enable script execution for JavaScript testing while being informed that external resources in preview may still initiate network requests.
Five starter templates — a complete HTML5 starter document, a semantic article, a responsive card, an accessible form, and a data table — load production-quality example markup instantly. A local validation panel checks for missing doctype declarations, unmatched tags, unclosed elements, missing image alt attributes, inline event handlers, and empty forms.
Common use cases
- Writing and previewing an HTML page while learning web development — see results instantly without a local server
- Editing a local .html or .htm file: open it in the browser, make changes, and download the revised copy
- Testing HTML and CSS snippets from a tutorial, Stack Overflow answer, or documentation example
- Creating semantic article pages, responsive card layouts, accessible forms, and data tables from starter templates
- Using the WYSIWYG visual pane to format headings, lists, and links without writing HTML tags by hand
- Formatting or minifying HTML markup before copying it into a CMS, email campaign, or deployment pipeline
- Reviewing common HTML structure warnings (missing doctype, unclosed tags, missing alt text) with the local validator
- Finding and replacing repeated text, class names, or attribute values across a long HTML document
Why use ToolsSonic's HTML Editor?
ToolsSonic's HTML Editor is differentiated from HTML5-Editor.net, HTMLCodeEditor.com, and HTML Online Viewer on four dimensions that matter for developers and privacy-conscious users.
No tracking, no ads, no localStorage: HTML5-Editor.net and HTMLCodeEditor.com use cookies, anonymous analytics, and tailored advertising. ToolsSonic contains zero analytics, zero advertising, zero cookies, and zero localStorage for editor content. Your HTML source is never transmitted to any server under any circumstances.
Three panes, one tool: HTML Online Viewer exposes only a source editor and preview panel. ToolsSonic adds a synchronized WYSIWYG visual editor as a third pane — matching the bidirectional workflow offered by HTML5-Editor.net but without that tool's advertising and tracking.
Sandboxed preview with explicit script control: Scripts are disabled by default in the preview iframe. An explicit toggle enables scripts for JavaScript testing, and the status bar explains that external resources may still make network requests. No competitor reviewed exposes this distinction explicitly.
Built-in validation diagnostics: HTMLCodeEditor.com and HTML Online Viewer have no visible validation panel. ToolsSonic's Validate action returns a diagnostic report with counts, descriptions, and specific element references — helping beginners and developers find structural problems before publishing.
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