CyberCalc is an open-source cybersecurity workbench for students, CTF players, and forensics work. It inspects bytes, hashes, encodings, XOR, endianness, subnets, and packet captures in the browser, and it can hand a result to CyberChef, Aperi’Solve, or Shark in one click. An opt-in open-weight model, openai-gpt-oss-20b, reads a short summary and suggests the next lab. The math stays local. The model never sees the API key and never replaces the calculations.