Node Debug Inspector

The problem

Print debugging fails when issues involve deep closures, unhandled promise rejections, or complex state that console.log cannot reach. Setting up a full IDE debugger often introduces too much friction or environment overhead for a quick probe.

What it does

• Attaches to running Node.js processes via the V8 Chrome DevTools Protocol (CDP).
• Sets targeted breakpoints and conditional pauses without modifying source code.
• Evaluates expressions directly within the local scope of a paused call frame.
• Generates CPU profiles to identify performance bottlenecks in hot endpoints.
• Walks call stacks to trace the origin of errors or hanging requests.

Frameworks & tools

Node.js (v22+ for native WebSocket support), Chrome DevTools Protocol (CDP), and curl.

Why this beats prompting it yourself

Manually constructing CDP JSON-RPC messages is error-prone and requires deep knowledge of the V8 inspector's internal methods. This skill automates the boilerplate for WebSocket handshakes and frame evaluation, providing immediate access to the process internals without manual protocol implementation.

Use cases

• Debug a hanging request by inspecting the state of unresolved promises.
• Recover variable values from private closures during a production-like crash.
• Verify execution paths in complex test suites without adding instrumentation.
• Capture CPU profiles of specific functions to resolve latency spikes.

Known limitations

Requires the Node.js process to be started with the --inspect flag or triggered via SIGUSR1. Native WebSocket support requires Node.js 22 or higher for the probe script.