Twilio - interview guide

Twilio interview questions - a complete guide

Twilio builds communication APIs for developers - so its interviews look at API design and reliability thinking alongside coding.

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About Twilio

Twilio provides APIs for SMS, voice calls, WhatsApp and email (SendGrid) - when an app sends you an OTP, there is often an API like this behind it. It has an engineering centre in Bengaluru. Fresher hiring is reported to vary from year to year.

This guide covers 12 Twilio interview questions with answers - what each question checks and how to answer it - plus the Twilio interview process, round by round, a 7-day preparation plan for freshers, tips and the mistakes to avoid.

Twilio hiring process

  1. HackerRank test

    Coding questions - reported as about 90-120 minutes.

  2. Technical screen

    Live coding and projects.

  3. Interview rounds

    Coding, a design discussion and a bar raiser behavioural round - depending on experience.

  4. Hiring manager

    Team fit and expectations.

Twilio does not publish its India fresher interview process in detail (as of our check). This is based on candidate reports - many of them for experienced roles, so the fresher process can differ. Confirm with the recruiter.

Sources (checked 16 October 2026): Twilio Careers. Hiring processes change - read the official notice before you apply.

Twilio interview questions and answers

APIs and reliability

  1. 1.Design an API for sending SMS - both send and delivery status.

    What they're checking
    Twilio's real product.
    How to answer
    POST /messages (to, from, body) returns a message id and 'queued' status at once; the actual sending happens in the background. Status (sent, delivered, failed) through GET or a webhook callback.

  2. 2.What is a webhook, and what do you do if the customer's server is down?

    What they're checking
    Event delivery.
    How to answer
    A webhook - when something happens, we send an HTTP request to the customer's URL. On failure, retry with exponential backoff, dead-letter after a limit, and sign it so the customer can verify the request came from us.

  3. 3.Design an OTP system - expiry, retries and protection against brute force.

    What they're checking
    Security + design.
    How to answer
    Store the OTP's hash (not plain text), 5-minute expiry, block after 3-5 wrong tries, a cooldown on resend, and a rate limit per number.

  4. 4.How do you make sure a retry doesn't send the customer the same SMS twice?

    What they're checking
    Duplicate delivery.
    How to answer
    A unique key with the request; the server first checks whether a message already exists for that key. Internal queue consumers also skip duplicates by message id.

  5. 5.One number is limited to 1 SMS per second - what about the other messages?

    What they're checking
    Rate limiting + queues.
    How to answer
    A separate queue per sender number; one worker takes one per second with a token bucket. If the queue gets too long, tell the customer or reject.

Coding

  1. 6.Split a long message into 160-character parts without cutting words in the middle.

    What they're checking
    String handling.
    How to answer
    Go word by word; if the current part + the word exceeds 160, start a new part. If a single word is longer than 160 it has to be split - mention that case.

  2. 7.Convert phone numbers to one standard format (E.164, like +919876543210).

    What they're checking
    Cleaning real data.
    How to answer
    Remove spaces, dashes and brackets; for a 10-digit Indian number starting with 0, drop the 0 and add +91; for 10 digits, add +91; error on a wrong length.

  3. 8.For every incoming message, say how many messages came in the last 60 seconds.

    What they're checking
    A sliding window on time.
    How to answer
    Keep timestamps in a queue; when a new one arrives, remove those older than 60 seconds from the front - the size is the answer. Each message goes in and out once.

  4. 9.Compress a string: 'aaabbc' -> 'a3b2c1'.

    What they're checking
    Writing basic code cleanly.
    How to answer
    Go along with a count and write it out when the character changes. Don't forget the last group at the end - that is the common mistake.

Bar raiser and values

Twilio's values include things like 'Wear the customer's shoes'.

  1. 10.When did you change your work by putting yourself in the customer's (or user's) place?

    What they're checking
    Customer focus.
    How to answer
    How you understood the user's problem, what you changed, and the difference.

  2. 11.Tell me about work where there was no path and you made the plan yourself.

    What they're checking
    Ownership in ambiguity.
    How to answer
    What wasn't known at the start, how you broke it down into a plan, and the result.

  3. 12.Why Twilio?

    What they're checking
    Motivation.
    How to answer
    If you have used an API like Twilio's (OTPs, notifications), that experience, and your interest in developer products.

7-day preparation plan for the Twilio interview

  1. Day 1: String and parsing problems.
  2. Day 2: Queues, sliding windows, rate limiting.
  3. Day 3: API design - REST, webhooks, retries.
  4. Day 4: OTP and notification system design.
  5. Day 5: Medium DSA - five problems, timed.
  6. Day 6: Values-based behavioural stories.
  7. Day 7: A mock interview.

Preparation tips

  • API design basics - status codes, idempotency, webhooks, retries.
  • Practise strings and sliding windows.
  • Specific stories with numbers for the bar raiser.
  • Take Twilio's free trial and send an SMS - it helps in the interview.

Mistakes to avoid

  • Not mentioning failure/retries in design.
  • Storing OTPs in plain text.
  • Treating the behavioural round as a formality.

Frequently asked questions

What is asked in the Twilio interview?

According to reports, HackerRank coding, live coding, a design discussion and a bar raiser behavioural round.

Does Twilio India hire freshers?

Fresher hiring is reported to vary by year - check current openings on the careers page.

Where is Twilio's India office?

An engineering centre in Bengaluru is reported.

What is Twilio's bar raiser round?

A behavioural round checking whether you will raise the team's level - questions on values and ownership.

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