Observatory : Observatory by Mozilla is a project designed to help developers, system administrators, and security professionals configure their sites safely and se...
mitmproxy : mitmproxy is your swiss-army knife for debugging, testing, privacy measurements, and penetration testing. It can be used to intercept, inspect, modify...
API Security Checklist : Checklist of the most important security countermeasures when designing, testing, and releasing your API.
Inj3ct0r 1337day.com : Exploit database separated by exploit type (local, remote, DoS, Poc, etc.)
XSS Filter Evasion Cheat Sheet - OWASP : This article is focused on providing application security testing professionals with a guide to assist in Cross Site Scripting testing.
This article explains what secure headers are and how to implement these headers in Rails, Django, Express.js, Go, Nginx, and Apache.