System design interview prep for senior engineers

Know exactly what to fix before you interview.

A live expert diagnoses you under real interview pressure. You get a hiring verdict against the bar for your level, the two or three things that drove it, and the moments to replay.

The problem

The interview went well. The email said no.

A real loop tells you no and never tells you why. A typical mock gives you a few minutes of feedback. The Diagnostic analyzes your every word and determines where to focus next.

• You remember the feeling, not the moments.

The report replays the exchanges that decided it, transcript and audio, so the hour stops being a mood.

• You didn’t get to hear what they actually thought.

Here the interviewer tells you what a real loop never does: what tipped the call, what they were waiting for, and where your work needs to go.

• You’re trying to learn everything at once.

You leave knowing the two or three things that cost you the verdict, instead of guessing across all of them.

The Formation Method

It starts with a human reading you under real interview pressure, and ends with a report built from what they found.

1. Step 01 · the hour

   Start with an expert mock to diagnose your gaps.

   A live, hour-long mock with a senior engineer who has run real hiring loops. You get what a real interview gives you — a hiring verdict — plus what it never does: structured feedback on exactly what drove it.

Diagnosis first, always.

Hiring verdict

This mock

Weak No

1. Strong No
2. No
3. Weak No
4. Weak Yes
5. Yes
6. Strong Yes

A hiring call on the scale a committee uses. Not a score.

2. Step 02 · after the hour

   Get a detailed report outlining where you need to focus.

   Your transcript and the interviewer’s structured feedback go through Nova, Formation’s AI. Out comes a gap report: the two or three things that actually moved the verdict, the evidence for each, and the moments to replay.

Not a scorecard. A short, ranked read with a reason attached to every claim — and the reason is always yours, never a template’s.

3. Step 03 · from there

   Close the gaps, with us or without us.

   Bring the report to the Fellowship and a mentor works the gaps it names with you until you land.

   Or keep it and work them yourself. It’s yours either way.

Your readiness by skill

Requirements & sizing
Interfaces & APIs
Data modeling
Storage & consistency
High-level Design
Scaling
Reliability
Production readiness
Design reasoning
Session leadership

Who runs the mock

Your mock is run by one of Formation’s mentors: engineers at top companies who run interviews for a living, at or above the level you’re targeting. Not a coach. Not a peer.

Formation’s mentors are engineers currently at

• OpenAI
• Netflix
• Google
• Meta
• Amazon
• Apple
• Stripe
• Uber
• Microsoft
• Airbnb

Under the hood

How the report gets written

Between your hour and your report sits a model of you. It reads every word and hesitation in the transcript, takes your mentor’s read, and reconciles the two against the bar for your level — attention a dedicated coach charges $400 an hour for.

What’s in your gap report.

Not a scorecard. The pattern a strong mentor would see after reviewing your session twice, laid out so you can act on it.

• Your hiring verdict

  A hiring call against the bar for your level — your mentor’s, not a score.

• What moved it

  The two or three things that drove it, ranked by how much each one weighed.

• Where it happened

  Every claim tied to a moment in the hour: transcript, audio, and what a strong answer would have sounded like.

• Your readiness by skill

  Every skill the hour could read, against the bar — and the ones it couldn’t, marked rather than guessed.

Pricing

Here’s what it costs.

The Diagnostic

New

$299

one-time

One live mock with a senior engineer at your target level, and a real hiring verdict

A gap report: the two or three things that drove the verdict, ranked by weight

Every concern tied to the moments it happened, with transcript, audio and what good looks like

Yours to keep. Nothing expires.

Credits in full toward the Fellowship within 90 days. Non-refundable.

Diagnostic questions

• Why a live mock instead of a quiz or an AI interview? Because pressure is the only honest test. A quiz measures what you know; a live hour with someone who runs real interviews measures what shows up when it counts. Nova reads the recording afterwards, but the interview and the verdict are human.

• How is the mock scored?
  The way real ones are: a hiring verdict from Strong No to Strong Yes, against the bar for the level you picked. Then the report ranks the two or three things that moved that verdict and ties each to the moments it happened. There’s no score out of 100 and no pass line. Real committees decide hire or no-hire; a percentage would be something we made up.

• Who runs the interview?
  One of Formation’s mentors: engineers at top companies who run interviews for a living, at or above the level you’re targeting.

• Which level is the mock run at?
  Senior or staff — you pick when you book. The verdict and the report read you against the bar for that level.

• Is the report written by a person or by AI?
  Both, with a clear split. Your mentor gives the verdict and structured feedback. Nova, Formation’s AI, reads the full transcript against that verdict to find the moments, rank what mattered, and write what good looks like. Every claim in the report points at a timestamp you can check. Your mentor files the verdict first, without seeing any of it.

• How soon do I get the report?
  Once your mentor has filed the verdict and the report is written. We email you the moment it’s ready, and it stays in your account.

• Does anything expire?
  The report doesn’t. No subscription, no expiry; it’s yours for the rest of your search. The one clock is the Fellowship credit: 90 days from your mock.

• Is training included?
  No. The Diagnostic tells you exactly what’s in the way and shows you what good looks like at each moment. Closing the gap is on you, or on us: the Fellowship is unlimited mentorship until you land, and the $299 counts toward it in full within 90 days.

• Can I get a refund?
  The mock is a live hour with a mentor, so once it’s run it can’t be undone and we don’t refund it. What you can do is put the $299 toward the Fellowship within 90 days.

• Can I do more than one?
  Yes. You can run another before a specific loop. If you want more than one or two, the Fellowship is the better deal: mocks are unlimited there.

• Why does it say New?
  Because the Diagnostic just launched as its own product. The mock is run by the same senior engineers as the rest of Formation. New means the packaging may change, not that the interview is practice for us.

Read enough? The mock is the next step.

One live mock, a report that names what’s actually in the way, and the moments to prove it. Yours to keep.

The Diagnostic · $299 · one payment · nothing expires

Run your diagnostic.