Shannon is a free, self-hostable AI pentester with 43,000+ GitHub stars that autonomously finds and exploits real vulnerabilities in your web apps and APIs, displacing manual security engagements that cost $15,000 to $50,000 per assessment. It scored 96% on the industry's standard benchmark and takes about ten minutes to install.

Shannon is a free, self-hostable AI security tool that autonomously finds and exploits real vulnerabilities in your web applications and APIs, displacing manual penetration testing engagements that typically cost $15,000 to $50,000 per assessment for a mid-market company. It crossed 43,000 GitHub stars in June 2026, which puts it among the fastest-rising security tools on the platform right now.

The short version: you point Shannon at a staging environment, give it your source code, and it behaves like a skilled attacker, reading your codebase, mapping how data flows, identifying where inputs get processed, and then trying to break in. It is not a scanner that flags potential issues and hands you a PDF. It runs actual exploits to confirm the vulnerabilities are real.

What Shannon actually does

Most security tools in this category are vulnerability scanners. They crawl your application, match patterns against known CVEs, and produce a report full of findings ranked by severity. The problem with scanners is that they generate a lot of noise. A finding that says "possible SQL injection at this endpoint" requires a human to verify whether it is actually exploitable, and that verification is most of what you are paying for in a manual pentest.

Shannon skips the theoretical and goes straight to proof. It operates in two modes that work together: static analysis on your source code to find attack vectors, and live exploitation against a running instance to prove they are reachable. It uses browser automation and command-line tooling to run the actual attacks, then validates that fixes close the holes before clearing them from the report.

On the XBOW Benchmark, the standard evaluation suite for web security tools, Shannon scored 96.15 percent in hint-free, source-aware mode, completing 100 of 104 exploit challenges. That is a specific, verifiable number against a specific test suite, which is more honest than most vendor marketing.

The business case for running this

A mid-market company doing an annual web application pentest for compliance, SOC 2 or PCI DSS reasons, typically pays $5,000 to $30,000 for that engagement depending on the size and complexity of the app. Large environments, multiple applications, or specialized cloud infrastructure push that number toward $50,000 and above. Most companies with any kind of customer-facing software should be running these tests at least once a year, and many frameworks now require quarterly validation.

Shannon does not eliminate the cost of a professional engagement if your compliance framework requires a signed attestation from an external firm. It does change the economics of the work your internal team can do. A developer can run Shannon against a new feature branch before it ships, catching exploitable issues before they reach a penetration tester's scope. Security teams can run it against staging as a pre-pentest cleanup pass, which reduces billable hours from the external firm because the obvious findings are already gone.

The honest version: Shannon probably does not replace your annual compliance pentest requiring a human signature. It does replace the ad-hoc security review your team was not running anyway because nobody had time.

The installation is actually simple

Shannon installs via npm. Running npx @keygraph/shannon setup handles the initial configuration. You then point it at your application with a URL and a path to your repository: npx @keygraph/shannon start -u https://your-staging-app.com -r /path/to/your-repo. It requires Docker and an Anthropic API key. The API key is the only recurring cost, and for individual assessments that cost is small compared to the test itself.

You can also clone the repository and build it locally if you want to audit what the tool is doing before giving it access to your codebase, which is reasonable given what it does.

What you need to understand before running it

Shannon comes with a blunt warning in its own documentation: this is not a passive scanner. The exploitation agents run actual attacks. Data gets modified. Logs get written. If you point this at a production environment, you will create real problems.

This means Shannon is a staging environment tool. You need a reasonably realistic copy of your app running in an environment where you can afford for things to break. For teams that already maintain a good staging environment, this is not a meaningful barrier. For teams running a minimal staging setup or sharing one across projects, getting the most out of Shannon requires some infrastructure work first.

The AGPL-3.0 license allows free use for internal security testing and self-hosted deployment. The copyleft requirement activates if you build a managed service on top of Shannon and offer it to others. For a company using Shannon to test its own applications internally, the license is effectively permissive. Keygraph also offers commercial licensing for organizations with specific requirements.

Shannon Lite is built for white-box testing, meaning it works best when you provide the source code. This is a tool for testing systems you own or have explicit permission to test. Using it on third-party systems you do not control is not what it is designed for.

There is also a coverage caveat. The 96 percent benchmark result reflects standardized challenges. Real production applications have unique business logic, non-standard authentication flows, and custom integrations. Shannon narrows the gap but does not close it. A skilled human pentester doing a focused engagement will still find things Shannon misses.

Who this is actually for

The most direct fit is a development or security team that wants to run continuous automated security validation against its own applications and currently has no way to do that without paying for an external engagement every time. If your company ships software quarterly and wants to understand its security posture without waiting for an annual pentest, Shannon gives you that loop at the cost of API tokens.

The second use case is pre-pentest hardening. If you have a scheduled external engagement coming up, running Shannon in the weeks before lets you close the obvious findings first, so the external firm spends its billable hours on complex, logic-level issues that actually require human expertise rather than on SQL injections you could have caught yourself.

Penetration testing has historically been expensive partly because it requires rare human expertise, and partly because manually validating every finding is real work. Shannon compresses that validation step. It does not replace expert judgment, but it changes the floor for what an internal team can accomplish before they need to call in outside help.

The price of knowing whether your application has an exploitable vulnerability is no longer a $20,000 conversation.