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Anthropic·Software Engineer·Technical Phone Screen·Senior

Senior
Jul 2026

Summary

Anthropic software engineer interview with a classic systems/algorithms question dressed up as a real product scenario. The crawler problem sounds approachable until you're actually in it and realize they want you to think about everything at once.

Questions Asked (1)

Q1

Build a single-threaded web crawler that starts from a given URL and collects all unique pages reachable within the same hostname. You're given a helper function that returns all hyperlinks on a page. Walk through your design choices: BFS vs DFS, how you parse the hostname, how you avoid cycles, and how you'd handle errors.

Algorithms & Data StructuresSystem DesignTechnical Trade-offs
Author's notes

I went with BFS mostly out of habit and then had to actually defend it, which I wasn't fully prepared for.

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AI HintsAI Generated

Suggested Approach

Start by clarifying requirements and constraints, then present a BFS-based crawler using a queue and a visited set to avoid cycles. Explain hostname parsing, error handling, and trade-offs between BFS and DFS, emphasizing politeness and scalability.

Pro tip: Mention that BFS is preferred for level-by-level crawling and early termination, but note that DFS uses less memory; also highlight the importance of respecting robots.txt and rate limiting to avoid overwhelming servers.

1. Clarify Requirements and Constraints

Ask about scale, politeness, and whether to respect robots.txt. Confirm that only pages with the same hostname should be crawled.

2. Choose BFS and Explain Why

Select BFS for its level-order traversal, which naturally handles cycles and allows early stopping. Contrast with DFS in terms of memory and use cases.

3. Design Data Structures and Hostname Parsing

Use a queue for BFS, a set for visited URLs, and parse hostnames via URL parsing libraries (e.g., urllib.parse). Normalize URLs to avoid duplicates.

4. Handle Errors and Edge Cases

Implement try-catch for network errors, timeouts, and invalid URLs. Skip non-HTML content and handle redirects carefully.

5. Discuss Trade-offs and Optimizations

Address memory vs. completeness, politeness (rate limiting), and potential improvements like concurrent crawling or distributed systems.

Key Points to Mention

  • BFS vs DFS: BFS for level-order and cycle avoidance, DFS for memory efficiency
  • Hostname parsing: use URL parsing libraries, compare hostnames exactly
  • Cycle avoidance: maintain a visited set of normalized URLs
  • Error handling: try-catch for network issues, timeouts, and invalid URLs
  • Politeness: respect robots.txt, rate limiting, and user-agent
  • Scalability: single-threaded limitations and potential for concurrency

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