Question 1Integrations and APIs
Walk me through connecting our product to a customer's internal system that has no documentation.
This happens weekly in the job. They want a calm, step-by-step method.
“Hands-on with APIs, webhooks, authentication (OAuth, SSO) and data integrations”Forward Deployed Engineer · Harmony
The answerFour steps
- 1
Find who owns the system and get read access to a test environment
Say it like this
“My first question is who owns it. Usually it's one person in IT, and I ask them for read access to a test copy.”
Why it scores
Starts with people. The owner knows the quirks no doc would list.
- 2
Watch real traffic or logs to learn the data shapes
Say it like this
“Then I watch real traffic for a few days, their own client's calls through a proxy or the database logs, and save a sample of every message shape.”
Why it scores
Learns from real traffic, not guesses. The saved samples become test fixtures.
- 3
Build a thin adapter with logging around every call
Say it like this
“I build a thin adapter that logs every request and response, with timeouts, so when something odd comes back I have the exact payload.”
Why it scores
Thin and logged. When it breaks, the payload is already there.
- 4
Agree on how failures get reported, and who fixes what
Say it like this
“Before go-live I agree with the owner: errors post to a shared channel, they fix their side, I fix the adapter.”
Why it scores
Splits ownership before the first failure, not during it.
StrongAll together
About a minute, out loud. The marked parts are the four steps; hover one to find it above.
Say it's a 15-year-old inventory system with a SOAP endpoint and no docs. My first question is who owns it. Usually it's one person in IT, and I ask them for read access to a test copy.1 Then I watch real traffic for a few days, their own client's calls through a proxy or the database logs, and save a sample of every message shape.2 I build a thin adapter that logs every request and response, with timeouts, so when something odd comes back I have the exact payload.3 Before go-live I agree with the owner: errors post to a shared channel, they fix their side, I fix the adapter.4
WeakThe answer that fails
Sounds fine. Common. Scores low.
“I'd look at the endpoints, try a bunch of requests in Postman to reverse-engineer the API, then write the integration code and test it until it works.”
Interviewer's note
Pokes the system alone. No owner, no logging, no plan for when it breaks.
PracticeTwo minutes, then they push back
Your turn
Walk me through connecting our product to a customer's internal system that has no documentation.
Answer like you're in the room: about two minutes, no notes. Say it out loud, even alone. It feels different from thinking it. Then check your answer against what interviewers score.