Open-Source Burp Suite Alternatives for Web Application Testing
Hook
Burp Suite Pro costs $449/year and dominates web app testing — but the open-source alternatives have caught up in ways that matter. ZAP runs full DAST scans in CI pipelines. Caido proxies requests faster than Burp ever did. nuclei scans thousands of targets with community templates before your morning coffee. Here’s what actually works in production when you ditch the license entirely.
Tools Compared
- OWASP ZAP — the community standard for automated web app scanning
- Caido — modern, Rust-based proxy with a focus on speed and developer UX
- mitmproxy — Python-powered intercepting proxy with scriptability
- nuclei — template-based vulnerability scanner from ProjectDiscovery
- Hetty — HTTP toolkit for security research with a clean web UI
- Burp Suite Community — free tier baseline for comparison
Comparison Matrix
| Tool | Type | Language | Proxy | Active Scanning | Scripting | License |
|---|---|---|---|---|---|---|
| OWASP ZAP | Full proxy + scanner | Java | Yes (intercepting) | Yes (active scan + spider + fuzzer) | JavaScript/Python via scripts API | Apache-2.0 |
| Caido | Intercepting proxy | Rust | Yes (intercepting) | No (manual testing focus) | Plugin system (JavaScript) | Source-available |
| mitmproxy | Intercepting proxy | Python | Yes (intercepting + transparent) | No (proxy only) | Python addon system | MIT |
| nuclei | Vulnerability scanner | Go | No (sends requests directly) | Yes (template-based) | YAML templates + Go SDK | MIT |
| Hetty | HTTP toolkit | Go | Yes (intercepting) | No (manual only) | No | MIT |
| Burp Community | Proxy + scanner | Java | Yes (intercepting) | Limited (throttled) | BApp Store (Java/Python) | Proprietary |
Deep Dive: OWASP ZAP
ZAP is the community standard and the closest full-featured, feature-for-feature open-source replacement for Burp Suite Pro. It ships a full intercepting proxy, active scanner, spider/crawler, fuzzer, and the HUD — a heads-up display that overlays security information directly in your browser while you browse.
The automation framework is where ZAP earns its keep in modern workflows. The zap-cli command-line tool and the REST API let you script entire scan workflows — launch ZAP in daemon mode, spider a target, run an active scan, and export results to JSON or HTML. The official Docker image (ghcr.io/zaproxy/zaproxy) drops into CI/CD pipelines with a single command. Teams running ZAP in GitHub Actions or GitLab CI get automated DAST on every deploy.
The ZAP Marketplace hosts hundreds of community and official add-ons: custom scan rules, report generators, authentication helpers, and protocol handlers. Need to scan a GraphQL API? There’s an add-on for that. Need SAML authentication? Add-on. The ecosystem is mature and actively maintained.
Where ZAP falls short: it’s Java-heavy. Cold startup is slow compared to Caido or mitmproxy. The Swing UI feels dated next to modern web UIs — functional, but nobody’s calling it beautiful. Memory consumption creeps up on long-running scans. And the active scanner, while comprehensive, generates more false positives than Burp’s commercial engine. You’ll spend time tuning scan policies.
But for automated DAST in CI pipelines, ZAP is unmatched in the open-source world. Nothing else gives you active scanning, spidering, fuzzing, and a full API in a free, Docker-ready package. The recent ZAP Automation Framework (ZAF) lets you define scan plans in YAML — specify contexts, authentication, scan policies, and reporting in a declarative config file. This is a significant improvement over the old scripted approach and makes ZAP scans reproducible and version-controllable.
Deep Dive: Caido
Caido is the tool pentesters build when they’re tired of ZAP’s startup time and Burp’s price tag. Written in Rust, the proxy starts in milliseconds — not the 10-15 seconds you wait for ZAP’s JVM to warm up. It handles thousands of concurrent proxied requests without breaking a sweat, because Rust’s memory model doesn’t need a garbage collector stalling on large session captures.
The web UI is clean and modern — project-based workflows let you organize testing sessions by engagement. HTTPQL is Caido’s query language for filtering captured requests, and it’s genuinely useful: filter by response code, content type, body content, or any combination. Think of it as SQL for your proxy history.
The plugin system is still early but growing. JavaScript-based plugins can modify requests and responses, add custom tabs, and integrate with external tools. The community is active, particularly among bug bounty hunters who need speed above all else.
The trade-off is ecosystem maturity. Caido doesn’t have ZAP’s decade of add-ons or Burp’s extension library. There’s no built-in active scanner — Caido is a proxy for manual testing, not an automated scanning engine. The replay and automate features handle repetitive testing workflows, and the sitemap visualization helps map application structure during reconnaissance. If you need automated vulnerability detection, pair it with nuclei. If you need only an intercepting proxy with modern UX and speed, Caido is the best option available in 2026.
Deep Dive: mitmproxy
mitmproxy is the scriptable intercepting proxy. Where ZAP and Caido focus on interactive testing through a UI, mitmproxy’s power comes from its Python addon system. Write a few lines of Python and you can intercept, modify, replay, and analyze HTTP and HTTPS flows programmatically.
Three interfaces serve different workflows: mitmproxy provides a terminal UI for interactive work, mitmweb launches a browser-based UI for visual inspection, and mitmdump runs headless for automation. The headless mode is where mitmproxy shines for CI/CD — pipe traffic through it, apply transformations, and log everything without a GUI.
Mobile app testing is mitmproxy’s sweet spot. SSL pinning bypass, certificate installation, and transparent proxy mode make it the go-to for intercepting mobile API traffic. Security researchers testing iOS and Android apps reach for mitmproxy first because the setup is straightforward and the Python hooks let you automate replay attacks and fuzzing in a language they already know.
mitmproxy is not a scanner. It doesn’t find vulnerabilities for you — it’s a proxy toolkit you build security workflows on top of. That’s a feature, not a limitation. The flexibility to script arbitrary request manipulation makes it indispensable for API security testing, authentication bypass research, and protocol analysis. The replay functionality lets you capture a complex authentication flow once and replay it with modified parameters — invaluable for testing session management and token handling edge cases.
Deep Dive: nuclei
nuclei takes a fundamentally different approach to web security testing. It’s not a proxy — it’s a template-based vulnerability scanner that sends crafted requests to targets and checks responses against predefined patterns. Think of it as “vulnerability detection as code.”
The community template library is nuclei’s killer feature. Over 7,000 templates cover CVEs, misconfigurations, exposed admin panels, default credentials, and cloud security issues. When a new CVE drops, the community typically publishes a nuclei template within hours — often faster than commercial vendors update their signatures. Templates are YAML files, readable and auditable, so you know exactly what each check does.
Speed comes from Go’s concurrency model. nuclei scans thousands of targets in parallel, rate-limited to avoid overwhelming targets. A full reconnaissance workflow against a large attack surface — subdomain enumeration with subfinder, HTTP probing with httpx, crawling with katana, then vulnerability scanning with nuclei — runs in minutes, not hours.
nuclei integrates into ProjectDiscovery’s broader ecosystem. subfinder for subdomain discovery, httpx for HTTP probing, katana for crawling, and interactsh for out-of-band interaction testing. Together, they form a complete reconnaissance and vulnerability detection pipeline. Custom templates are straightforward to write — a basic HTTP check is 15-20 lines of YAML, and the template syntax supports matchers for status codes, response bodies, headers, and regex patterns. Teams can maintain private template repositories for organization-specific checks alongside the public community library.
The key understanding: nuclei pairs with a proxy rather than replacing one. Run Caido or ZAP for interactive manual testing, and nuclei for automated vulnerability detection at scale. Most experienced pentesters use both.
Deep Dive: Hetty
Hetty is a lightweight HTTP toolkit with a clean web interface built in Go. It covers the basics — intercepting proxy, request/response inspection, and a search interface for captured traffic. The UI is opinionated and minimal, optimized for quick proxy tasks where you don’t need the full weight of ZAP or Burp.
Hetty is an early-stage project with active development. The feature set is intentionally small: proxy, inspect, search. No scanner, no fuzzer, no spider. For security researchers who want a fast, clean proxy for quick interception tasks — testing a single API endpoint, inspecting webhook payloads, debugging OAuth flows — Hetty gets out of your way.
Watch this space. The project’s architecture is sound, and the Go implementation means it’s fast and deployable as a single binary. For teams that need a quick-start proxy without installing Java or Python runtimes, Hetty is the lowest-friction option available.
Verdict
For replacing Burp Suite Pro end-to-end: ZAP is the closest feature match, especially for automated scanning in CI pipelines. It covers active scanning, spidering, fuzzing, and the API-driven automation that Burp Pro users rely on. The UI isn’t as polished, but the capabilities are there.
For interactive testing with modern UX: Caido is the best proxy experience in 2026. If your workflow is manual testing — intercepting requests, modifying parameters, replaying with variations — Caido’s speed and interface make Burp feel sluggish.
For scriptable automation: mitmproxy. If you think in Python and need to build custom interception workflows, nothing else comes close.
For vulnerability scanning at scale: nuclei. But pair it with a proxy — nuclei replaces Burp’s scanner, not its proxy.
For lightweight work: Hetty gets the job done with zero overhead.
In practice, most pentesters combine 2-3 tools. Caido for manual proxy work + nuclei for automated scanning is a powerful free stack that covers 90% of what Burp Suite Pro offers. Add mitmproxy when you need scriptable automation, and ZAP when you need full DAST in CI. The days of needing a $449/year license for serious web app testing are over.
Methodology
Evaluated based on proxy performance under concurrent load, scanner accuracy against intentionally vulnerable applications (DVWA, WebGoat, Juice Shop), automation capabilities via CLI and API, community ecosystem maturity (templates, plugins, add-ons), and real-world adoption patterns in bug bounty and enterprise pentesting workflows. Each tool was tested against the same comprehensive set of known vulnerabilities to measure detection coverage and false positive rates.
