Buildthetechnicalreasoningbackendinterviewstest.
Practice interview-relevant concepts with adaptive questions, answer-specific explanations, spaced review, and simulated production debugging cases.
Built by an SDE interview tutor who coaches candidates for North American interviews.
Cache invalidation: which strategy guarantees readers never see stale data after a write completes?
Topics you can practice
Debug Detective
Practice debugging through simulated production incidents.
Investigate simulated outages using the same tools you'd reach for at work — terminal, logs, metrics, distributed traces. Gather evidence, form a hypothesis, identify the root cause. Scored on the correctness of your final diagnosis and how efficiently you reach it.
- 9 cases scaling from junior to senior — start with latency mysteries, advance to distributed transactions and resource-pool exhaustion.
- Diagnosis-and-efficiency scoring — based on final-diagnosis correctness and the time taken to reach it.
- Try 3 cases free — full 9-case curriculum on Premium.
p95 latency
0↑
DB queries/req
0↑
Error rate
0→
Distributed trace
db.queries (25× SELECT) — 7.9s
How it works
Turn interview prep into a focused practice loop.
Choose an interview-relevant track
Start with System Design, OOD, backend fundamentals, networking, databases, or AWS. Concept relationships keep prerequisite context visible as you practice.
Test the mental model
Use multiple-choice, true/false, and fill-in-the-blank questions. When you get stuck, use guided hints; after a miss, review an explanation tied to the answer you chose.
Revisit what needs work
Each session updates your review queue and concept history. Track recent accuracy, revisit missed concepts, and continue into related practice.
What makes it different
Practice, feedback, and review in one focused loop.
Adaptive engine
Adaptive difficulty responds to recent answers
Every answer adjusts the next question. Strength areas advance. Weaker concepts branch into targeted practice before they harden into blind spots.
Sessions increase difficulty when your recent answers stay stable.
Missed concepts loop back into targeted practice and the review queue automatically.
What updates in real time
Answer-specific feedback
See the concept behind a missed answer.
Use guided hints while you solve, then get a concise explanation tied to the answer you chose.
Practice history
See what your practice data is showing.
Accuracy, review history, and concept progress help surface what to practice next.
Review queue
Return to the right concepts at the right time
Missed and aging concepts are scheduled into one queue, so you can keep practicing without building your own spreadsheet.
Last studied 9 days ago · Review is due
Recent answers support a harder problem
Recent answers are stable — no review due now
System Design library
Read deeply, then practice immediately
Study guides with a clean reading flow, open unfamiliar terms in plain language, then jump straight into related questions.
Rate Limiter
Token bucket allows bursty traffic while keeping average throughput bounded.
Jargon: token bucket
Q: Which rate limiting algorithm allows short bursts while holding a stable average rate?
Concept checks
Test the mental models behind interview answers
Use multiple-choice, true/false, and fill-in-the-blank questions to check understanding from several angles.
Concept graph + knowledge map
Navigate prerequisites with confidence
Visual concept dependencies show prerequisite relationships and concepts worth revisiting before deeper topics.
Session progress
Review your session activity at a glance
Review the concepts affected by a session, queued reviews, and the related practice available next.
Before session
After session
Memory science
Review the right concepts before they fade.
Delta Byte schedules missed and aging concepts into your review queue, so you can revisit them without managing a spreadsheet.
Without Delta Byte
With Delta Byte
Illustrative review schedule—not a measured Delta Byte outcome. Individual retention varies.
Pricing
Choose the practice plan that fits your interview timeline.
Free plan
- Daily quizzes — 10 / day
- Spaced repetition review
- Progress dashboard
- Session history
- System Design library — Starter access
Premium
$14.08/mo · Save 30%
- Daily quizzes — Unlimited
- Adaptive difficulty
- Progress Report
- Plain-language term explainer
- Guided hints and explanations
- System Design library — Full catalog access
- Debug Detective — All 9 cases
Build the technical judgment backend interviews look for.
Start with interview-relevant concept practice and see what to review next.