ATOM Signatures publishes two free tools that run in your browser here: an email signature banner resizer and a checker for the HTML of an Outlook signature. No account is needed, and the image or HTML you use is not sent to any server: the processing happens on your computer.
In short: these tools solve one case at a time, on one image or one signature. To roll out and maintain the same signature for every Microsoft 365 employee, see the guide to managing signatures in Microsoft 365 instead.
The tools
- Email signature banner size — load an image, get it at 600 px wide (or 1200 px at double resolution), see it at 320 px wide and download the PNG.
- Email signature checker for Outlook — paste a signature's HTML: hosted, embedded or attached images, SVG, width, code size and dark-mode contrast, with the guide that explains each problem.
What happens to my image and my HTML?
Nothing leaves your browser. The resizer reads the file you chose and redraws it on the spot; the checker analyses the pasted HTML on the spot and shows its preview in an isolated frame that runs no script. Neither tool sends your content to a server; the checker's preview only loads hosted images, from their own address, as the recipient would.
All pages in this section
- Email signature banner size for Outlook and mobile
Resize an email signature banner for free to 600 px (or 1200 px @2x), see it at 320 px and download it, with nothing sent anywhere. - Free email signature checker for Outlook
Paste a signature's HTML: hosted or embedded images, SVG, weight, width and dark mode. Each error links to its guide. The check runs in your browser.