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Fencer and RunSybil both run autonomous AI penetration tests that prove a vulnerability by exploiting it. RunSybil is a black-box pen tester for web apps and APIs: it finds and proves vulnerabilities, then hands you a fix to apply yourself. Fencer proves exploits and then applies the fix, opening pull requests for code and correcting cloud misconfigurations through the provider API, and it runs inside a platform that secures your whole stack, at published pricing.
Lean software teams that want fast, autonomous pen testing which proves exploits and then fixes issues, across the whole stack, at published pricing.
Teams that want a black-box pen tester, who have the budget and resources to remediate findings themselves.
The core of AI penetration testing is whether the tool actually exploits a vulnerability to prove it is real, rather than flagging a theoretical issue. Both tools do this.
Finding and proving a vulnerability is half the job; remediation is the other half. This is where the two tools differ most.
Coverage is which parts of your stack the tool tests and secures. A narrow scope leaves the rest to other tools; a broad platform consolidates find and fix in one place.
Black-box testing sees only what an external attacker can reach; white-box also sees code and configuration, catching issues a black-box run cannot. The strongest coverage uses both.
Cadence is how often the tool tests. It decides whether coverage keeps pace with how often you deploy.
Whether pricing is published tells a lean team if it can evaluate without a sales cycle.
| Criterion | Fencer | RunSybil |
|---|---|---|
| Proves exploits | Yes, end to end with evidence and a PDF report | Yes, black-box, with reproduction steps |
| Fixes the vulnerabilities | Applies fixes: pull requests for code, cloud misconfigurations corrected directly | Recommends a fix (a prompt for your own coding agent) |
| Attack surface | Whole stack via the platform (code, dependencies, secrets, containers, cloud, network, app, domains, SaaS) | Web and API against a live URL |
| Testing style | Black-box and grey-box, plus white-box platform visibility | Black-box by design |
| Cadence | On-demand and continuous | Continuous (every pull request or a set cadence) |
| Severity discipline | High or critical only when actually exploited | Validated findings |
| Pricing | $3,000 one-time or included on platform plans | Demo and quote only |
| Built for | Lean software teams, no security engineer required | High-velocity software teams |
Fencer is the better fit for a lean software team that wants autonomous pen testing to prove what is exploitable and then close it, across the whole stack, without a dedicated security engineer. Proof-of-exploit routes straight into applied fixes (pull requests for code, cloud corrections), testing runs on-demand or continuously, and pricing is published.
RunSybil is the better fit for a team that wants focused black-box web and API pen testing, has the budget and in-house resources to remediate findings itself, and runs separate tools for code, dependency, and cloud coverage.
