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Anthropic·Software Engineer·Technical Phone Screen·Senior

Senior
Jun 2026

Summary

Anthropic software engineering interview where they drop you into an existing codebase and ask you to add a new endpoint while also hunting down pre-existing bugs. More realistic than a whiteboard problem, but also more stressful because there's a lot going on at once.

Questions Asked (1)

Q1

You're given a skeleton API server with existing endpoints, middleware, and a data layer. Add a new endpoint per the provided spec, wire up routing, validation, and proper response codes, and make sure tests are updated.

API & IntegrationsTechnical Trade-offsSystem Design
Author's notes

The hardest part wasn't adding the endpoint itself.

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AI HintsAI Generated

Suggested Approach

Start by thoroughly understanding the existing codebase structure, including how routes are defined, middleware is applied, and the data layer is accessed. Then, implement the new endpoint following the established patterns, ensuring validation and proper response codes are handled consistently. Finally, update and run tests to verify functionality and catch regressions.

Pro tip: Before writing any code, read the spec carefully and clarify any ambiguities with the interviewer. Also, look for existing similar endpoints to reuse patterns and avoid reinventing the wheel.

1. Understand the spec and codebase

Review the endpoint spec and explore the existing code to identify routing, middleware, validation, and data access patterns. Ask clarifying questions if needed.

2. Design the endpoint implementation

Plan how to structure the handler, including input validation, business logic, and response formatting. Decide where to place the code to match existing conventions.

3. Implement routing and validation

Add the route to the appropriate router, apply any necessary middleware, and implement input validation (e.g., using existing validation libraries or custom logic).

4. Handle responses and errors

Ensure the endpoint returns correct status codes (e.g., 200, 201, 400, 404, 500) and consistent error response bodies. Use existing error handling middleware if available.

5. Update and run tests

Write or update unit and integration tests for the new endpoint, covering success and failure cases. Run the full test suite to ensure no regressions.

Key Points to Mention

  • Follow existing code patterns and conventions for consistency.
  • Validate input thoroughly and return appropriate 4xx status codes for client errors.
  • Use proper HTTP status codes (e.g., 201 for resource creation, 200 for successful GET).
  • Ensure error responses are consistent with the rest of the API.
  • Write tests for both happy path and edge cases, including validation failures.
  • Consider security aspects like authentication, authorization, and input sanitization.

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