Runtime Debugging Skill

Capture runtime data from instrumented fetch calls. Use when you need to understand what's happening at runtime - variable values, execution flow, timing, or state changes.

When to Use

• Debugging async/await issues or race conditions
• Tracing state changes across function calls
• Capturing variable values at specific execution points
• Understanding control flow through complex code paths

Workflow

Step 1: Create Debug Server

Run the bundled server script:

Start it:

node "${CLAUDE_PLUGIN_ROOT}/scripts/debug-server.js" 3333 &

Verify:

curl http://localhost:3333/health

Step 2: Instrument Code

Insert fetch calls at strategic locations:

fetch("http://localhost:3333/debug", { method: "POST", headers: { "Content-Type": "application/json" }, body: JSON.stringify({ label: "your-label", data: { key: value } }) }).catch(() => {});

Placement examples:

Function entry/exit:

async function processOrder(orderId) {
  fetch("http://localhost:3333/debug", { method: "POST", headers: { "Content-Type": "application/json" }, body: JSON.stringify({ label: "processOrder-entry", data: { orderId } }) }).catch(() => {});
  // ...
  fetch("http://localhost:3333/debug", { method: "POST", headers: { "Content-Type": "application/json" }, body: JSON.stringify({ label: "processOrder-exit", data: { result } }) }).catch(() => {});
  return result;
}

Error handling:

catch (error) {
  fetch("http://localhost:3333/debug", { method: "POST", headers: { "Content-Type": "application/json" }, body: JSON.stringify({ label: "error", data: { message: error.message, stack: error.stack } }) }).catch(() => {});
  throw error;
}

Step 3: Ask User to Reproduce

Tell the user:

"I've added debug instrumentation. Please reproduce the issue now, then let me know when done."

Step 4: Analyze Logs

cat .claude-debug/debug.log

Look for:

• Timestamps showing execution order
• Unexpected values
• Missing entries (code paths not taken)
• State inconsistencies

Step 5: Cleanup

pkill -f "debug-server.js"
rm -rf .claude-debug/

Remove the fetch instrumentation from the code.

Label Conventions

Pattern	Example	Use For
fn-entry	processOrder-entry	Function start
fn-exit	processOrder-exit	Function end
error	error-auth	Caught errors
state	state-before	State changes
branch	branch-early-return	Control flow