Ad Specs Tester is a browser based tool for validating digital advertising creatives against publisher specifications. It supports image, video, audio, and HTML5 zip file formats. The tool checks a creative against over 4,000 placements from major publishers including Facebook, Instagram, and TikTok. A defining characteristic of the application is that all processing occurs locally within the user's browser; no files are uploaded to external servers. The user workflow involves dropping a creative file or pasting XML into the interface. The tool evaluates the creative against the selected placement's requirements, checking dimensions, file size, format compatibility, safe zones, and copy limits. For HTML5 creatives, the tool runs the code in a sandboxed frame for up to 30 seconds to monitor loaded resources, errors, and animation behavior. The application fetches ad tags and wrappers directly through the user's browser to simulate a live ad environment. If a publisher's ad server does not allow direct browser fetching due to CORS restrictions, the user can paste the XML instead. Typical use cases include preflight quality assurance for ad operations teams, creative agencies, and developers who need to ensure their assets meet specific publisher guidelines before trafficking. The tool provides a detailed report highlighting discrepancies between the creative and the placement specifications. Access to the tool is free, with a daily limit on checks. Users can sign in with their email to increase the daily check limit to 50, with no password required.