Subtrace is a zero-code network tracer for backend servers. Started with a single command, it captures every incoming and outgoing HTTP request in real time - payload, headers, latency, and status - and shows them in a Chrome DevTools-style interface. It uses eBPF to do this without code changes or root privileges, so engineers can find, inspect, and replay production requests instead of grepping through scattered logs. The tool is open source (BSD-3-Clause) and came out of Y Combinator's Winter 2025 batch.

Brendan Gregg is an Australian systems performance engineer at OpenAI, where he works on datacenter optimizations for ChatGPT. He invented flame graphs and the USE Method, pioneered eBPF observability, and is the author of landmark books including 'Systems Performance: Enterprise and the Cloud'. His work is credited with saving the industry over $1 billion in compute costs. Previously an Intel Fellow and performance engineering leader at Netflix, Gregg is one of the most influential engineers in Linux and cloud infrastructure.