Tools Viewer apps ship with open-source components that make the editors and compilers work in the browser. Below are the primary libraries used by live tools today. Your drafts and previews stay on your device unless you copy or export them yourself. This page is attribution and reference — not legal advice.
We list each major dependency with a link to the upstream project and its license text so engineers, educators, and compliance reviewers can verify terms without digging through the bundle. Marketing pages do not load these libraries; they appear with the interactive tool UI after you open a live app.
HTML Viewer Pro
Live HTML editor with split preview, formatting, minification, validation, diff, and element inspect linking. Open the tool at HTML Viewer Online. Ace powers the code panels; js-beautify helps format HTML when you ask the tool to tidy markup. Together they support the free online HTML viewer workflow described in our HTML Viewer Pro guide.
- Ace Editor (ace-builds) — code editor and syntax highlighting (Ace license text)
- js-beautify — HTML formatting (js-beautify license text)
Email Viewer
HTML and MJML email preview with client-style simulations, CSS inlining, and local QA. Open HTML Email Preview or browse email templates. Ace provides the editor surface; mjml-browser compiles MJML to HTML in your tab. Those components enable the workflows in the Email Viewer guide without requiring you to install a local MJML toolchain.
- Ace Editor (ace-builds) — editor surface (Ace license text)
- MJML (mjml-browser) — MJML to HTML compilation in the browser (MJML license text)
RegEx Visualizer
Pattern testing, match highlighting, explanations, and replace previews run as Tools Viewer application code in your browser. Open RegEx Visualizer or read the RegEx Visualizer guide. When additional third-party packages are introduced for this tool, they will be listed here with links to their license texts so this page stays the single attribution index for live apps.
How we use these libraries
Libraries load with the interactive tool UI so editing stays client-side. Marketing pages do not eagerly load Ace or MJML. Coming-soon tools may add dependencies later; this page will grow when those apps go live. For product privacy wording, read the Privacy Policy. Using Tools Viewer does not change the upstream licenses — you still follow Ace, js-beautify, MJML, and any future packages on their own terms when you redistribute their code.
Questions about Tools Viewer branding, site reuse, or attribution for our own content belong on the Contact page. Questions about an upstream library belong with that project’s maintainers and license file.
Related: Privacy Policy · Terms of Service · Contact · Guides
Frequently asked questions
Why does ToolsViewer list open-source licenses?
Live tools reuse libraries such as Ace Editor, js-beautify, and MJML. This page points to their license texts so you can review attribution and terms.
Does using Ace or MJML upload my content?
No. Those libraries run in your browser as part of the tool UI. Core editing and preview stay on your device unless you export content yourself.