Julius: LLM Service Fingerprinting
How Julius, Praetorian's open-source tool, identifies the LLM serving software, such as Ollama or vLLM, behind an endpoint.
What is LLM Service Fingerprinting?
LLM service fingerprinting identifies what server software is running on a network endpoint—not which AI model generated text, but which infrastructure is serving it.
Julius answers the question: "Is this HTTP service an LLM?" During a penetration test or attack surface assessment, you’ve found an open port. Is it Ollama? vLLM? A Hugging Face deployment? Some enterprise AI gateway? Julius tells you in seconds.
Julius follows the Unix philosophy: do one thing and do it well. It doesn’t port scan. It doesn’t vulnerability scan. It identifies LLM services—nothing more, nothing less.
This design enables Julius to slot into existing security toolchains rather than replace them.
Introducing Julius
Julius is an open-source LLM service fingerprinting tool that detects 17+ AI platforms through active HTTP probing. Built in Go, it compiles to a single binary with no external dependencies.
Probes Included in Initial Release:
Self-Hosted LLM Servers
Proxy & Gateway Services
Cloud-Managed Services
RAG & Orchestration Platforms
Generic Detection
What's Next
Julius is the first tool release of our “The 12 Caesars” open source tool campaign where we will be releasing one open source tool per week for the next 12 weeks. Julius focuses on HTTP-based fingerprinting of known LLM services. We’re already working on expanding its capabilities while maintaining the lightweight, fast execution that makes it practical for large-scale reconnaissance.
On our roadmap: additional probes for cloud-hosted LLM services, smarter detection of custom integrations, and the ability to analyze HTTP traffic patterns to identify LLM usage that doesn’t follow standard API conventions. We’re also exploring how Julius can work alongside AI agents to autonomously discover LLM infrastructure across complex environments.
Contributing & Community
Julius is available now under the Apache 2.0 license at https://github.com/praetorian-inc/julius
We welcome contributions from the community. Whether you’re adding probes for services we haven’t covered, reporting bugs, or suggesting new features, check the repository’s CONTRIBUTING.md for guidance on probe definitions and development workflow.
Ready to start? Clone the repository, experiment with Julius in your environment, and join the discussion on GitHub. We’re excited to see how the security community uses this tool in real-world reconnaissance workflows. Star the project if you find it useful, and let us know what LLM services you’d like to see supported next.
For more information on Julius, check out the Praetorian Blog!
Still need help? Ask the team