Stripe·Software Engineer·Technical Phone Screen·Intermediate

IntermediatePrefer not to say

May 2026

Summary

Stripe SWE interview where they hand you a broken JSON parser and tell you to fix it. No scaffolding, no hints, just read the code and figure out what's wrong. Felt like a real debugging shift more than a coding interview.

Questions Asked (1)

You're given a working-ish JSON parser implementation that handles the full spec (objects, arrays, strings, numbers, booleans, null, escape sequences). It has multiple bugs. Identify and fix all of them.

Root Cause AnalysisTechnical Trade-offsAlgorithms & Data Structures

Author's notes

This one took me a while to even get my footing.

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AI HintsAI Generated

Suggested Approach

Start by understanding the parser's architecture and the JSON spec, then systematically test each component with edge cases to uncover bugs. Prioritize fixes based on severity and impact, and verify each fix with targeted tests to ensure correctness.

Pro tip: Demonstrate a methodical debugging process by writing tests first to reproduce bugs, and communicate your reasoning clearly as you go. This shows engineering maturity and makes your problem-solving transparent.

1. Understand the Code and Spec

Review the parser's structure and compare it against the JSON specification to identify potential areas of deviation. Clarify any ambiguities about expected behavior with the interviewer.

2. Write Tests to Reproduce Bugs

Create a comprehensive set of test cases covering all JSON features and edge cases (e.g., nested structures, escape sequences, number formats). Run them to identify failing cases and pinpoint bugs.

3. Prioritize and Fix Bugs

Categorize bugs by severity (e.g., crashes vs. incorrect parsing) and fix them one by one, starting with critical issues. Explain your reasoning for each fix and consider potential side effects.

4. Verify Fixes and Refactor

Re-run tests to ensure all bugs are fixed and no regressions are introduced. Refactor code if necessary to improve clarity or performance, but avoid over-engineering.

5. Discuss Trade-offs and Improvements

Summarize the bugs found, the fixes applied, and any trade-offs made (e.g., performance vs. readability). Suggest further improvements or edge cases to handle.

Key Points to Mention

Thorough understanding of the JSON specification, including escape sequences and number formats.
Systematic debugging approach: reproduce, isolate, fix, verify.
Importance of edge cases: empty objects/arrays, deeply nested structures, unicode characters, etc.
Trade-offs between performance and code simplicity when fixing bugs.
Writing unit tests to prevent regressions and ensure correctness.
Clear communication of thought process and reasoning throughout the interview.

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.