ESAPI is a product of the Open Web Application Security Project (OWASP). The organization collects expertise on securing web applications, holds conferences and develops tools such as the WebScarab HTTP/S analysis proxy. OWASP members range from small consulting firms and security providers like Symantec to industry giants like IBM and Microsoft.

ESAPI describes methods that a typical web app needs for security. These methods include fixing authentication and protecting against cross-site scripting (XSS), cross-site request forgery (XSRF) and SQL injection. Other methods address failure to restrict URL access, insecure communications and improper error handling. The project publishes a Top 10 list of the most serious web app vulnerabilities.

ESAPI has an OWASP API for each of the top ten web app vulnerabilities.

The ESAPI project recommends that developers shouldn't continue to reinvent the security wheel for each application, but base their efforts on OWASP's expertise gained "over a decade of code review and penetration testing of critical enterprise applications."

The API is virtually independent of operating system and programming language, even though the current reference implementation is written in Java along with its Javadoc. Versions for .NET and PHP are planned.

ESAPI's Java implementation requires Java 1.4.2, but Java 1.6 users can uncomment code to make it work for them. The reference implementation is in binary JAR format for downloading. Developers will then have a forum in the OWASP-ESAPI mailing list.