5 technical interview questions with model answers — practise the English vocabulary and structure of strong FastAPI Developer responses.
0 / 10 completed
1 / 10
The interviewer asks: "Why does async/await matter in FastAPI, and when should you use it?" Which answer best demonstrates FastAPI Developer expertise?
Option B is strongest because it covers concurrency without threads, the ASGI/Starlette foundation, how FastAPI handles sync routes via thread pool executor, the CPU-bound limitation with ProcessPoolExecutor, and the critical rule about not blocking inside coroutines. Option A is incorrect — claiming async is always faster and recommending universal async def usage would cause issues when calling synchronous blocking code inside coroutines. Option C correctly identifies use cases but doesn't explain the mechanism or the when-NOT-to-use-async caveat, which is what distinguishes intermediate from advanced knowledge. Option D discusses the GIL at length, which is technically adjacent but not relevant to the async/await question in FastAPI context — it reads like a Python internals tangent. FastAPI Developer interview best practice: always mention that regular def routes run in a thread pool executor, not inline — this surprises many candidates and shows depth.
2 / 10
The interviewer asks: "How does Pydantic improve data handling in FastAPI applications?" Which answer best demonstrates FastAPI Developer expertise?
Option B is strongest because it covers type-annotation-driven validation with concrete examples (EmailStr, Field constraints), the 422 response, automatic JSON serialisation, OpenAPI doc generation, and the Pydantic v2 Rust performance improvement — showing awareness of the current ecosystem. Option A makes a comparison to Marshmallow that is loosely true but signals the candidate knows Marshmallow better than Pydantic; FastAPI interviews expect Pydantic-native knowledge. Option C explains the basic validation flow correctly but misses serialisation, OpenAPI integration, and Field() constraints — a partial answer. Option D focuses entirely on v1-to-v2 migration syntax without explaining why Pydantic matters or how it improves data handling, which is what was actually asked. FastAPI Developer interview best practice: mention that FastAPI uses Pydantic models to auto-generate the OpenAPI schema — this demonstrates you understand the full developer experience benefit.
3 / 10
The interviewer asks: "Can you describe FastAPI's dependency injection system and its advantages?" Which answer best demonstrates FastAPI Developer expertise?
Option B is strongest because it explains Depends(), automatic sub-dependency graph resolution, the generator/yield pattern for session management, dependency_overrides for testing, async dependency support, and lifespan management — a complete and practical answer. Option A conflates FastAPI's parameter parsing (path, query, body) with the dependency injection system; these are different mechanisms and mixing them up signals a surface-level understanding. Option C correctly identifies Depends(), request-scoped caching, and two use cases, but misses the testing override capability which is a major advantage and what separates FastAPI DI from simple function parameters. Option D draws a Spring comparison that may confuse the interviewer and doesn't add information about FastAPI's actual capabilities — cross-framework comparisons belong only at the end of an answer, not as the main content. FastAPI Developer interview best practice: always mention app.dependency_overrides — it's the feature that makes FastAPI DI genuinely testable.
4 / 10
The interviewer asks: "How would you implement OAuth2 authentication with JWT tokens in FastAPI?" Which answer best demonstrates FastAPI Developer expertise?
Option B is strongest because it covers the full FastAPI implementation: OAuth2PasswordBearer, python-jose for JWT encoding/decoding, exp and sub claims, passlib/bcrypt for password hashing, the get_current_user dependency pattern, and OAuth2PasswordRequestForm — a complete and deployable picture. Option A recommends third-party libraries, which may be valid in production but in an interview context signals an unwillingness to explain the underlying mechanism; interviewers want to know you understand OAuth2+JWT, not that you can install a package. Option C explains JWT structure accurately but is completely framework-agnostic — the interviewer asked about FastAPI specifically and this answer would fit any language or framework. Option D focuses exclusively on refresh token implementation, which is a valid advanced topic but skips the fundamental access token flow that was actually asked about. FastAPI Developer interview best practice: lead with OAuth2PasswordBearer and the Depends pattern — it shows you know the FastAPI-idiomatic approach, not just generic JWT knowledge.
5 / 10
The interviewer asks: "How would you compare FastAPI to Flask and Django in a technical interview?" Which answer best demonstrates FastAPI Developer expertise?
Option B is strongest because it frames each framework's strengths clearly (async-first + OpenAPI for FastAPI, batteries-included for Django, minimal flexibility for Flask), ties the comparison to use case, mentions performance benchmarks in context, and ends with a sound principle — choose based on needs not novelty. Option A is a common candidate mistake: claiming FastAPI is always the best choice shows bias and lack of nuance, which an experienced interviewer will push back on immediately. Option C correctly identifies Django's ORM and admin advantage but gives an incomplete comparison — Flask isn't mentioned and there's no performance context or decision framework. Option D is factually wrong claiming all three use WSGI (Flask is WSGI, FastAPI is ASGI, Django supports both) and drifts into async history without providing a clear recommendation structure. FastAPI Developer interview best practice: structure the comparison as a decision matrix, not a ranking — this demonstrates you can advise a team rather than just advocate for your favourite tool.
6 / 10
Code Review Comment: Sarah, during a review of the user authentication endpoint, you've added this comment: 'This code doesn't handle rate limiting. Users could potentially flood the system.' Which of the following responses best addresses Sarah's concern and demonstrates an understanding of FastAPI best practices?
The correct answer demonstrates an immediate understanding of Sarah's feedback and proposes a relevant solution using a standard FastAPI extension. Options A and B are either too simplistic or dismissive of the issue. Option C correctly identifies a specific tool for rate limiting, while option D shows a lack of technical knowledge and requests clarification – which is appropriate in a code review setting but not the core response.
7 / 10
Slack Message: You're part of a team discussing an API response from a third-party service. The response contains a large array of nested JSON objects with many fields. David asks you, 'How can I efficiently handle this data in my FastAPI application?' Which of the following is the MOST appropriate reply?
Pydantic is specifically designed to handle complex JSON structures by defining models that enforce data types and validation rules. This prevents errors and makes working with the data much more robust. Options A and C are overly simplistic and don't address potential issues. Option D suggests relying on the external service, which isn't a best practice for error handling or data integrity.
8 / 10
PR Description: You're creating a pull request to add an endpoint that retrieves user profiles. The description reads: 'This PR adds the ability to get user data from the database.' Which of the following additions would significantly improve this description and demonstrate better developer communication?
A good PR description should provide specific details about what the change *does*. Simply stating 'It returns a JSON object…' doesn't convey the actual functionality or the data format. Option A provides technical detail, while options B and C are too vague, and option D is a general statement that doesn't add value to the PR description.
9 / 10
Standup Update: During your daily standup, you're asked about your progress on implementing user authentication. You say, 'I'm working on the OAuth2 flow.' Which of the following statements best describes what you should have communicated to provide a more complete update?
A standup update should focus on *what* you're doing and *where* you are in the process. Saying 'I'm researching…' is vague. Specifying that you're integrating with Google and Facebook provides concrete information about the work being undertaken. Options A and C are too high-level, while option D suggests a lack of progress.
10 / 10
Code Review Comment: You receive the following comment on a FastAPI endpoint function: 'This function doesn't handle potential errors gracefully – it just returns a 404 if something goes wrong.' Which of the following best explains how you should respond to this feedback, demonstrating your understanding of FastAPI?
The original comment correctly identifies that the function *does* use HTTP status codes for error handling. A better response would involve enhancing this by providing detailed information about the error within a JSON response, following best practices for API design and improving debugging capabilities. Option A is a valid approach but doesn't address the need for informative error messages.
What does "FastAPI Developer Interview Questions — English Practice" cover?
Practise English for FastAPI Developer technical interviews: 5 scenario-based questions with model answers and vocabulary explanations.
How many questions are in this interview set?
This set has 10 exercises, each with a full explanation.
Is this exercise free to use?
Yes. Every exercise on CoderSlingo, including this one, is free to use with no account, sign-up, or paywall.
Do these exercises include model answers?
Yes. Each interview question gives you several possible responses and asks you to pick the one that communicates most clearly and completely — the explanation then breaks down exactly why that answer works, including the specific vocabulary a strong candidate would use.
What if I choose an answer that isn't the strongest one?
You'll see which option was correct and read a full explanation of why it's stronger than the alternatives, plus the key vocabulary and phrasing worth reusing in a real interview.
Can I retry the questions?
Yes — use the "Try again" button on the results screen to reset and go through the set again.
Is this the same as a real technical or behavioural interview?
No — it's focused practice for the language side of interviewing: recognising which phrasing sounds precise and confident versus vague, and knowing the vocabulary interviewers expect for this role. It won't replace mock interviews, but it builds the vocabulary you'll need in one.
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Who writes these interview questions?
Every question is written by the CoderSlingo team based on real technical interview patterns for this role, then reviewed for accuracy and clarity.