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InSitu supports two production debugging workflows. You can place and inspect probes manually in VS Code, or let an MCP-connected coding agent investigate an incident and produce an evidence-backed Root Cause Analysis (RCA). Both workflows use the same runtime instrumentation and safety controls without a restart, redeployment, or debugger stop.

The Probe Lifecycle

Choose how you want to drive the investigation:
1

Set a Probe in VS Code

Right-click any line in an open source file and choose a probe type — Snapshot, Log, Counter, Metric, or Tic & Toc. The extension registers the probe definition with the broker.
2

SDK Agent Retrieves the Probe

The SDK agent polls the broker for active probes and dynamically instruments the target line in-memory. This happens live, with no process restarts.
3

Capture Runtime Data

When execution hits the instrumented line, the SDK agent captures variables, logs, counters, or metrics without stopping the application in a debugger.
4

Enqueue and Flush Telemetry

Captured telemetry is queued in a bounded in-memory buffer and flushed to the broker in asynchronous batches. Network I/O stays off the application request path.
5

Inspect Results in VS Code

The extension fetches the captured data and renders it inside your editor’s InSitu panel, presenting variable trees and call stacks.

Runtime Instrumentation Mechanics

InSitu does not modify your source files or your deployed build artifacts. Instead, it hooks into the runtime’s native introspection capabilities:
  • Node.js (V8): The Node SDK connects to the V8 debugger runtime using the native inspector protocol. It places virtual break-hooks on specific compiled script locations. When hit, the callback grabs the local scope and call stack, returning control in microseconds.
  • Java (JVM): The Java Agent attaches via the standard -javaagent flag. It performs lightweight, runtime bytecode manipulation using byte code libraries to inject capture instructions on-the-fly.
  • Python (CPython): Python 3.12 and later uses sys.monitoring. Python 3.7–3.11 instruments selected function bytecode in memory. Both capture data on the application thread and enqueue telemetry for asynchronous delivery. Neither rewrites source files or uses sys.settrace.
Because instrumentation happens at the engine layer, InSitu maps compiled output back to original source coordinates seamlessly as long as source mappings (Node.js) or debug symbols (Java) are provided. No special handling required in Python.

Architectural Topology

The VS Code extension and MCP-connected coding agents are two developer clients for the same InSitu backend. Both create probes through the broker and consume telemetry captured by the in-process SDK agent.
InSitu architecture for VS Code and MCP clients

Built-In Safety Guardrails

The SDK agent runs a safety monitor alongside your host application to help limit resource contention and performance impact:
  • Overhead Suspension: Safety checks depend on the SDK. When a safety limit is crossed, the agent can suspend probes and resume them after a cooldown. See the Python SDK guide for Python thresholds.
  • Global Throughput Throttling: Limits the maximum number of captures per second. Hits beyond this ceiling only increment the execution counter and bypass data serialization to save resources.
  • Strict Payload Boundaries: Snapshots are restricted by maximum object depth, array length, and string size to ensure minimal memory usage.
  • Local and Global Hit Limits: Each probe has a configurable hit limit. Once reached, its instrumentation is automatically and instantly uninstalled.