Caido is a web proxy and HTTP traffic inspection toolkit for security researchers, penetration testers, and bug bounty hunters who need granular, real-time control over browser-to-server communication. Built on a Rust backend with a browser-rendered interface, it competes directly with Burp Suite but takes a decidedly leaner, more modern architectural approach.
What is Caido?
Caido is a local web proxy that intercepts every HTTP and HTTPS request passing between your browser and a target server, giving you the power to pause, inspect, modify, and replay that traffic mid-flight. Unlike older-generation tools that lean on Java runtimes and UI paradigms from a different decade, Caido renders its interface in a browser tab and runs its core engine in Rust — a combination that means near-instant startup, a clean layout, and a resource footprint that barely registers in Activity Monitor during a heavy testing session.
Installation on macOS via Homebrew Cask takes under a minute. Once Caido is running, you point your browser's proxy settings at its local listener and requests start arriving in the intercept queue immediately. The first-run experience is genuinely polished: CA certificate installation is guided step-by-step, and the HTTPQL filter syntax is explained inline rather than buried in an external wiki.
What does Caido do best?
The Replayer is where Caido earns its keep in daily manual testing. Capture any request, send it to Replayer with a single keystroke, modify headers, parameters, or body content, then fire it — the response diff view highlights exactly what changed between the original and your modified version. Anyone who has spent cumulative hours managing Burp's Repeater tabs will feel the ergonomic improvement immediately.
The Automate module extends manual replay into scripted attack sequences: drive a parameter through a wordlist, chain dependent requests that extract values from prior responses, and collect results in a sortable, filterable table. It is not as feature-complete as Burp Intruder, but the friction is significantly lower and findings surface cleanly. Beyond those headline features, a few capabilities round out the toolkit nicely:
- HTTPQL filtering — a structured query language for slicing large traffic captures by host, method, status code, or body content without endless scrolling
- JavaScript plugin hooks — extend Caido's behaviour at the request/response level without waiting on a core release
- Project workspaces — scope traffic captures to a specific engagement so sessions never bleed into each other
How much does Caido cost?
Caido is free to download, and the community plan covers the core proxy, interceptor, replayer, and automation tooling — more than enough for independent security research and solo bug bounty work. Paid tiers add cloud project sync, team collaboration features, and expanded workflow capabilities. Pricing updates periodically, so check caido.io directly for current figures rather than trusting any cached number you find in a forum thread.
Who should use Caido?
Caido is built squarely for web penetration testers, application security engineers, and bug bounty hunters. If your daily work centres on REST APIs, GraphQL endpoints, OAuth flows, or multi-step authenticated web sessions, it fits naturally into the toolkit from day one. Students and career-changers breaking into web security get real value from the free tier — the HTTPQL language and intercept workflow teach HTTP semantics more viscerally than any textbook chapter. It is not the right tool for raw network-layer analysis (that's Wireshark territory) or for wide-surface automated scanning where Burp Professional's active scanner still leads.
How does Caido compare to Burp Suite?
Burp Suite Professional remains the enterprise benchmark: a mature active scanner, a sprawling BApp Store extension library, and deep CI/CD pipeline integrations that Caido cannot yet match. If your engagement requires a scanner or a niche Burp extension, you still need Burp in the mix.
For the majority of manual testing work — intercepting, replaying, fuzzing, and annotating — Caido is faster to start, lighter on RAM, and far less punishing to look at for extended sessions. Burp's free community edition deliberately hobbles key features; Caido's free tier does not. OWASP ZAP is a solid free alternative if automated scanning is your priority, though its interface demands patience. Proxyman is excellent for macOS HTTP debugging but targets developers inspecting their own APIs rather than testers probing third-party targets. Many practitioners I know now keep both Caido and Burp installed, reaching for Caido as the day-to-day default and switching to Burp only when the scanner or a specific extension is essential.
