Senior Engineer Interview Preparation Guide (L5+ / Staff)

I got promoted to Senior Engineer, then immediately started failing interviews for Senior roles at other companies.

The problem: I was preparing like a junior candidate. More LeetCode problems, faster solving. But Senior interviews test different things—and I was studying for the wrong exam.

After adjusting my approach and passing Senior interviews at two different companies, here's what I learned about how L5+ interviews actually work.

The uncomfortable truth: Senior interviews aren't harder junior interviews. They're a different evaluation entirely. System design matters more. Behavioral goes deeper. And coding expectations shift from "can you solve it?" to "can you solve it the way a senior would?"

One-Minute Decision: L5+ Prep Strategy

If you're L4 going to L5:
Focus 40% on system design, 30% on coding (with emphasis on communication), 30% on behavioral. Your coding is assumed to be good—you need to prove you can design systems and lead.

If you're L5 going to Staff/L6:
Focus 50% on system design, 25% on behavioral (with leadership depth), 25% on coding. System design at scale and organizational impact in behavioral are the differentiators.

If you're interviewing at FAANG vs. startups:
FAANG: Standard leveling, expect rigorous system design. Startups: May weight coding more heavily; system design may focus on their specific domain.

Don't make junior-level mistakes:

• Grinding 500 LeetCode problems (you need depth, not volume)
• Preparing generic behavioral stories (you need leadership and influence)
• Treating system design as optional (it's 40-50% of Senior interviews)
• Optimizing only for coding speed (communication matters more at senior level)

How Senior Interviews Differ

The Bar Shift: What Changes at L5+

What Senior Interviewers Actually Evaluate

In Coding Rounds:

• Do you clarify requirements before coding? (Seniors do this automatically)
• Do you discuss trade-offs, not just solutions?
• Can you communicate your thinking as you go?
• Do you catch edge cases before being prompted?
• Do you write clean, production-quality code?

In System Design Rounds:

• Do you structure the conversation (requirements, estimates, design)?
• Do you make and justify trade-off decisions?
• Do you consider scale, reliability, and failure modes?
• Do you know when to go deep vs. stay high-level?
• Can you adapt when the interviewer pushes back?

In Behavioral Rounds:

• Do your stories involve leading, not just participating?
• Do you demonstrate influence without authority?
• Do you show impact at team or org level?
• Do you own failures and articulate learnings?
• Do you show technical judgment and decision-making?

Quick Verdict Table: L5+ Resources

System Design: The Senior Difference

What L5+ System Design Looks Like

Junior approach:
"I'll use a database and a server. Here's the basic structure."

Senior approach:
"Let me clarify requirements first. What's our expected QPS? Read-heavy or write-heavy? What's our latency target? What's our availability requirement?"

Then:
"Based on these constraints, here are the trade-offs we need to make..."

The L5+ System Design Framework

1. Requirements Clarification (5-7 minutes)

• Functional requirements: What does the system do?
• Non-functional requirements: Scale, latency, availability
• Constraints: Budget, team size, timeline

2. Back-of-Envelope Estimates (3-5 minutes)

• Users/QPS/storage calculations
• This shows you think about scale

3. High-Level Design (10-15 minutes)

• Core components and data flow
• Database choices (SQL vs. NoSQL, why?)
• Caching strategy (what, where, why?)

4. Deep Dives (10-15 minutes)

• Interviewer-directed or self-chosen
• Show expertise in specific areas
• Discuss failure modes and mitigation

5. Trade-offs and Alternatives (5 minutes)

• What would you do differently with more time/resources?
• What are the risks of your design?

The Designs You Must Know for L5+

Common L5+ System Design Mistakes

Mistake #1: Jumping to solution without clarifying requirements

What happens: You design for the wrong constraints
The fix: Always spend 5+ minutes on requirements, even if it feels slow

Mistake #2: Only giving one option

What happens: Interviewer thinks you don't know alternatives
The fix: "We could use X or Y. Given our constraints, I'd choose X because..."

Mistake #3: Not knowing your numbers

What happens: "I guess we'll need... some servers?"
The fix: Practice back-of-envelope estimation. Know common scales (1M users, 10K QPS, etc.)

Mistake #4: Ignoring failure modes

What happens: Design looks good until interviewer asks "what if this fails?"
The fix: Proactively discuss single points of failure and mitigation

Coding: Pattern Mastery vs. Problem Quantity

The Senior Coding Bar

At junior level: "Did they get the right answer?"
At senior level: "Did they approach this like a senior engineer?"

What that means:

1. Requirements first: Do you ask clarifying questions?
2. Approach discussion: Do you discuss multiple approaches before coding?
3. Trade-off awareness: Do you articulate time/space trade-offs?
4. Code quality: Is your code clean, readable, maintainable?
5. Communication: Do you explain your thinking as you code?
6. Testing: Do you verify with examples and edge cases?

How Many Problems for L5+?

The anti-pattern:
"I'll solve 500 problems to be ready for Senior interviews."

The reality:
I've seen engineers solve 500+ problems and fail Senior interviews because they couldn't communicate their approach. I've also seen engineers solve 100 problems well and pass easily.

The L5+ recommendation:

• 100-150 problems total
• Focus on pattern mastery, not volume
• Practice explaining your approach out loud
• Time yourself, but communication matters more than speed

Problem Approach for Seniors

Step 1: Clarify (1-2 minutes)

• Edge cases?
• Input constraints?
• Can I modify input?

Step 2: Approach Discussion (2-3 minutes)

• "I see a few approaches here..."
• "The brute force would be O(n²), but I think we can do better with..."
• Get buy-in before coding

Step 3: Code (15-20 minutes)

• Narrate as you code
• Write clean, modular functions
• Handle edge cases explicitly

Step 4: Verify (3-5 minutes)

• Walk through examples
• Discuss complexity
• Mention optimizations

Behavioral: Leadership Stories at Scale

What L5+ Behavioral Looks Like

Junior behavioral: "Tell me about a project you worked on."
Senior behavioral: "Tell me about a time you led a team through ambiguity."

The difference: Scope and ownership.

The Stories You Need for Senior Roles

Behavioral Story Selection for L5+

Your stories should demonstrate:

• Scope: Team-level or cross-team impact, not just individual
• Ownership: You led, not just participated
• Influence: You convinced others, not just executed orders
• Judgment: You made trade-off decisions, not just followed a plan
• Growth: You improved processes, not just completed tasks

Red flags in senior behavioral answers:

• "My manager told me to..." (lack of autonomy)
• "The team decided to..." (unclear personal ownership)
• "It was successful" with no metrics (unquantified impact)
• Only individual contributor stories (no leadership evidence)

The Staff+ Behavioral Bar

What's different at Staff+:

• Organizational impact: Did you change how the company operates?
• Cross-team leadership: Did you align multiple teams?
• Technical strategy: Did you set technical direction, not just execute?
• Mentorship: Did you develop other engineers?
• Business awareness: Do you connect technical decisions to business outcomes?

Staff+ specific story types:

• Driving a technical initiative across 3+ teams
• Mentoring engineers who got promoted
• Changing a company-wide process or standard
• Making a build vs. buy decision with significant impact
• Resolving an organizational conflict

The Staff+ Interview Difference

What Changes at L6/Staff

Staff+ System Design Expectations

Beyond senior-level design:

• Multi-region considerations
• Cost vs. performance trade-offs
• Organizational constraints (team ownership)
• Evolution over time (v1 vs. v2 vs. v3)
• How to break down implementation across teams

Staff+ Behavioral Expectations

The questions change:

• "Tell me about a time you influenced company direction"
• "How have you developed technical leaders?"
• "Describe a technical strategy you defined"
• "When have you made a significant build vs. buy decision?"

Timeline by Current Level

L4 → L5 Transition

Timeline: 8-10 weeks typical

Time allocation:

• System design: 40%
• Coding: 30%
• Behavioral: 30%

Focus areas:

• System design from "familiar" to "comfortable"
• Behavioral stories with team leadership
• Coding clarity and communication

Common gaps to address:

• System design depth (most L4s don't have enough)
• Leadership stories (need team-level examples)
• Trade-off articulation (need to discuss options)

L5 → L6/Staff Transition

Timeline: 10-14 weeks typical

Time allocation:

• System design: 50%
• Behavioral: 30%
• Coding: 20%

Focus areas:

• System design at massive scale
• Behavioral stories with org-level impact
• Cross-team leadership examples

Common gaps to address:

• Scale reasoning (handling 10M+ users, 100K QPS)
• Org impact stories (beyond direct team)
• Technical strategy articulation

External vs. Internal L5+ Interviews

Internal transfers:

• May skip some rounds (your work is known)
• Behavioral focuses on new team fit
• System design may test specific domain
• Usually faster process

External interviews:

• Full loop with all rounds
• Need to prove everything from scratch
• More standardized evaluation
• Longer process with more interviewers

Common Senior Interview Mistakes

Mistake #1: Preparing Like a Junior

What happens: Grinding 400 LeetCode problems, ignoring system design
The problem: L5+ is 40-50% system design. You're studying for 30% of the test.
The fix: Allocate time proportionally. System design and behavioral matter as much as coding.

Mistake #2: Generic Behavioral Stories

What happens: "I worked on a project and it was successful."
The problem: No leadership, no metrics, no ownership demonstrated.
The fix: Every story needs: your specific role, quantified impact, decision-making shown.

Mistake #3: Not Practicing System Design Out Loud

What happens: You know the concepts but stumble during the interview.
The problem: System design is a live design session, not an exam.
The fix: Practice with another person. Record yourself. Get feedback on your structure.

Mistake #4: Optimizing Only for Speed

What happens: You solve coding problems fast but can't explain your thinking.
The problem: Senior bar includes communication, not just correctness.
The fix: Practice narrating your thought process. Do mock interviews.

Mistake #5: Underestimating Behavioral Depth

What happens: "I'll prep behavioral the week before."
The problem: Senior behavioral is rigorous. You need 8-10 strong stories mapped to competencies.
The fix: Start behavioral prep at the halfway point. Practice out loud.

What People Ask About Senior Prep

"I'm a Senior at my current company. Why am I failing Senior interviews elsewhere?"

Short answer: Internal role ≠ interview performance. Interviews test specific skills that your daily job may not exercise.

Common reasons:

• Your company's bar is different from interview company's bar
• You haven't practiced system design or coding recently
• Your behavioral stories aren't framed for interviews
• You're out of practice with timed problem-solving

The fix: Treat external interviews as a different skill that requires specific preparation.

"Should I apply for L5 or L6 externally?"

Decision framework:

• Apply for L6 if: You're already L6, or high-performing L5 with Staff scope stories
• Apply for L5 if: You're L5 and want a safer path
• Be aware: Some companies down-level. Apply for what matches your stories.

The negotiation angle: You can apply for L6 and accept L5 offer with downlevel if needed. Harder to apply for L5 and negotiate up to L6.

"How is FAANG system design different from startup system design?"

FAANG expectations:

• Scale: Design for millions of users
• Reliability: 99.99%+ availability, failure handling
• Standardized format: Clear requirements → estimates → design → deep dive

Startup expectations:

• Practical: Design for their specific scale
• Domain-focused: May be very specific to their product
• Flexibility: May care more about speed to market

"Do I need to know every system design pattern?"

Short answer: No. You need to know 8-10 core designs well, not 30 designs superficially.

The must-knows: URL shortener, feed system, chat, CDN/streaming, cache, rate limiter
The nice-to-knows: Search, notification, payment, booking system
The bonus: Whatever is relevant to target company's domain

Final Verdict: The L5+ Prep Stack

After failing senior interviews with junior prep and then passing with adjusted approach, here's what I learned:

The Mistakes I Made

Mistake #1: 200 more LeetCode problems will help

• Reality: I already had the coding skills. I lacked system design depth.
• Lesson: At senior level, system design is 40-50% of evaluation.

Mistake #2: My work experience IS my behavioral prep

• Reality: My stories weren't structured for interviews.
• Lesson: Stories need framing: ownership, impact, learnings.

Mistake #3: System design is intuitive, I'll figure it out

• Reality: Structured approach matters. I rambled.
• Lesson: Practice the framework out loud with others.

The Prep Stack That Worked

For L5 (8-10 weeks):

For Staff/L6 (10-14 weeks):

One-Minute Decision Guide

If you're L4 → L5:
Focus 40% on system design. Your coding is assumed good—prove you can design.

If you're L5 → Staff:
Focus 50% on system design, 30% on behavioral with org impact. Coding is maintenance.

If you're failing senior interviews:
You're probably over-investing in coding and under-investing in system design and behavioral.

If you have 4 weeks or less:
Prioritize system design and behavioral. Do coding pattern refresh, not deep practice.

Last updated: January 12, 2026. Based on my own L5+ interview journey—failing with junior prep, adjusting, and passing—plus conversations with hiring managers about what the senior bar actually looks like. The level expectations described reflect common patterns across top tech companies as of Jan 2026; specific companies may vary.