Following definitions is easy to begin and surprisingly hard to finish. One function leads to a helper, the helper leads to an interface, and a few minutes later you know a great deal about an abstraction without knowing what happens when the user clicks the button.

A useful trace keeps the original question visible. It follows the calls that explain a behavior and records the state that decides which path runs.

Give the trace a boundary

Write down where the behavior starts and what result would answer your question. “From a request arriving to a response being returned” is a boundary. “Everything related to requests” is not yet one.

Choose a representative input. If the system has several configurations, identify the one you are tracing. A development-mode handler may take a very different path from a production-mode handler even when their entry point is the same.

Record each meaningful transition

Keep a small table or note as you read:

receiveRequest(input)
  → validateInput(input)
  → resolveHandler(config.mode)
  → handler.execute(validatedInput)
  → formatResponse(result)

For each transition, record the source location and the value that selects the next step. In this example, config.mode matters because it determines which implementation runs.

Skip through trivial wrappers only after checking that they do not add behavior. A wrapper may inject authentication, translate errors, schedule work, or change cancellation semantics.

Distinguish possible calls from actual calls

Definition and reference tools are excellent locators. They do not always tell you which target runs for a specific input.

Suppose a registry maps names to handlers:

const handlers = {
  local: new LocalHandler(),
  remote: new RemoteHandler(),
};

const handler = handlers[config.mode];
return handler.execute(input);

Finding both execute implementations establishes the possible paths. To choose one, trace where config.mode comes from and whether it can be overridden. Defaults, environment configuration, user preferences, and request-level values may all participate.

If you cannot establish the selected value, keep both paths in your explanation and name the missing evidence.

Mark asynchronous handoffs

An await, callback, event, or queued job can interrupt the apparent straight line between two functions. Record who holds the state while work is suspended and how the result returns.

Consider what may change during that interval. A newer request could arrive. The active document could close. Cancellation could be requested. A result may still be valid as data but no longer valid for the current user interface.

Look for the condition that accepts or rejects the result: a request identifier, revision number, ownership check, or another explicit invariant. If there is no such condition, determine whether the caller’s contract makes it unnecessary before concluding that it is missing.

Trace the return and failure paths too

The forward calls tell only part of the story. Follow the result back through the callers. Does each layer preserve the error, convert it, retry, or hide it?

A failed operation may still leave a side effect. A cancelled task may stop future work without undoing a write. Keep those distinctions visible when explaining the outcome.

Tests, logs, and a controlled runtime observation can help resolve questions that static reading leaves open. State which kind of evidence you have for each conclusion.

Stop when you can explain the behavior

You have a useful trace when you can describe the entry point, the path-selection conditions, the important state changes, the result, and the relevant failure boundary.

You will still have unexplored helpers. That is fine if their internal details do not affect the current question. Keep a short list of the assumptions you relied on and the follow-ups that would change the conclusion.

In Yenpo, keep the entry file in a tab while following definitions and references. Use the AI reader to ask where a value came from or why a branch ran, then inspect the linked source. The conversation is most useful when it helps you keep the thread in your own hands.