Every modern browser ships with a built-in developer toolkit. For hacking, it's your first line of investigation — before you even think about external tools. Press F12 (or Ctrl+Shift+I on Windows / Cmd+Option+I on Mac) on any webpage to open it.

The panels you need to know

• Elements — the live HTML structure of the page. You can edit it in real-time. Modify prices, remove disabled attributes, reveal hidden fields.
• Console — a live JavaScript REPL. Run JS directly against the page. Read cookies, manipulate the DOM, test XSS payloads.
• Network — every HTTP request the page makes. See exactly what's being sent and received, including API calls that happen in the background.
• Application — cookies, localStorage, sessionStorage, IndexedDB. All the data stored by the site in your browser.
• Sources — the JavaScript files loaded by the page. Search for hardcoded API keys, secrets, interesting endpoints.

Right-click → Inspect

Right-clicking any element on a page and selecting "Inspect" jumps straight to that element in the Elements panel. Faster than hunting through the HTML tree manually.