Question 1
Difficulty: medium
How do you design a PHP application so it stays maintainable as the codebase grows?
Sample answer
I start by separating responsibilities as early as possible. In practice, that means keeping business logic out of controllers, using services or action classes for workflows, and letting models focus on data access. I also prefer dependency injection so components are easier to test and replace later. When a project grows, consistent naming, clear folder structure, and small methods become just as important as the framework itself. I’m careful about introducing abstractions only when they solve a real problem, because overengineering can make a codebase harder to read. For maintainability, I also value automated tests, code reviews, and a clear convention for error handling and validation. In one project, I helped reduce duplicated logic by extracting shared payment rules into a dedicated service layer, which made new features faster to implement and safer to change. My goal is always to make the next developer’s job easier, including my own.
Question 2
Difficulty: medium
What steps do you take to improve the performance of a PHP application?
Sample answer
I usually approach performance in layers, starting with measurement rather than assumptions. First, I look at slow endpoints, database queries, and repeated work in the request cycle. If the bottleneck is the database, I check for missing indexes, N+1 queries, and queries that can be simplified or cached. On the PHP side, I reduce unnecessary object creation, avoid heavy logic in loops, and make sure any external calls are minimized. I also pay attention to caching at the right level, whether that’s application caching, response caching, or background jobs for expensive tasks. For example, on one project we improved page load times by caching frequently requested reference data and optimizing several ORM queries. I also like to monitor memory usage and use profiling tools when needed. Performance work is most effective when it is systematic, because the real gain usually comes from fixing the biggest bottleneck, not the smallest micro-optimization.
Question 3
Difficulty: medium
How do you handle database interactions in PHP to avoid common issues like SQL injection and poor query design?
Sample answer
I treat database access as something that needs both safety and discipline. To prevent SQL injection, I rely on prepared statements or framework query builders rather than concatenating raw input into SQL. I also validate and sanitize data before it reaches the database layer, although parameter binding remains the main protection. For query design, I try to keep queries readable and efficient by selecting only the columns needed, using indexes wisely, and avoiding repeated queries inside loops. If a report or feature requires complex filtering, I prefer to shape the query carefully instead of fetching too much data and filtering in PHP. I also pay attention to transactions when multiple writes must succeed together, because partial updates can cause hard-to-debug data issues. In a recent feature, I refactored a slow search flow by replacing several small queries with a single optimized one and added pagination to keep response times stable. My focus is on correctness first, then efficiency.
Question 4
Difficulty: hard
Tell me about a time you had to debug a difficult PHP issue in production. How did you approach it?
Sample answer
When I debug a production issue, I try to stay calm and work from evidence rather than guessing. In one case, users were reporting intermittent failures during checkout, but the error did not appear consistently in development. I started by checking logs, request traces, and recent deployments to identify patterns. The issue turned out to be related to a race condition between two requests updating the same order state. Once I understood that, I reproduced the behavior locally by simulating concurrent requests and confirmed the root cause. I then added a transaction and locking strategy to protect the critical section, and I also improved logging so future failures would be easier to diagnose. What I learned from that experience is that production debugging is as much about narrowing the problem as it is about fixing it. I always try to leave the system more observable than I found it, so the next issue is easier to solve.
Question 5
Difficulty: medium
How do you ensure your PHP code is testable, and what types of tests do you usually write?
Sample answer
I design for testability by keeping logic modular and minimizing hidden dependencies. That means injecting services instead of creating them inside methods, and avoiding large controller methods that mix validation, business rules, and persistence. For testing, I usually start with unit tests around business logic that should behave consistently across different inputs. Then I add integration tests for database interactions, API calls, and key workflows where multiple parts of the system need to work together. I don’t try to test every line equally; I focus more coverage on areas where regressions would hurt the business. In one project, adding tests around discount calculation caught edge cases that had been slipping into production during promotions. I also like tests that are readable and tell a clear story, because brittle tests can slow down delivery instead of helping it. My view is that good tests give the team confidence to refactor, which is essential for any PHP application that keeps evolving.
Question 6
Difficulty: medium
How would you handle a requirement to integrate a third-party API into a PHP application?
Sample answer
I’d start by understanding the API behavior, including authentication, rate limits, error formats, and timeout expectations. Before writing code, I like to define how the integration should behave when the external service is slow or unavailable, because that is where many problems show up later. In the implementation, I would isolate the API client into its own service so the rest of the application does not depend directly on request details. I’d also make sure requests are retried only where it makes sense, especially for non-idempotent operations. Logging is important too, because if the API misbehaves, we need enough detail to trace what happened without exposing sensitive data. I once integrated a shipping provider API where failures were common during peak hours, so I added queued retries and fallback messaging for users. That made the checkout flow much more resilient. My goal is always to make the integration reliable, observable, and easy to replace if the vendor changes later.
Question 7
Difficulty: hard
What is your approach to working with legacy PHP code that is difficult to read or refactor?
Sample answer
With legacy code, I try to improve things without breaking what already works. My first step is to understand the current behavior by reading the code, checking logs, and writing tests around the existing output before changing anything major. If the code is messy, I look for small, safe improvements first, such as extracting repeated logic, renaming unclear variables, or isolating a risky section behind a simpler interface. I avoid a full rewrite unless there is a strong reason, because rewrites often take longer and introduce new bugs. In one legacy system I worked on, the authentication flow was tightly coupled to old session code. Instead of replacing everything at once, I introduced a wrapper layer, added tests, and gradually moved users onto a cleaner implementation. That approach let the team deliver features while reducing risk. I like legacy work because it rewards patience and good judgment, not just technical skill.
Question 8
Difficulty: medium
How do you handle security concerns in a PHP application beyond SQL injection?
Sample answer
I treat security as part of everyday development, not a separate checklist at the end. Beyond SQL injection, I pay close attention to authentication, authorization, CSRF protection, password hashing, file upload validation, and session handling. For passwords, I use strong hashing methods provided by the platform rather than custom logic. For authorization, I make sure access checks happen server-side and are enforced consistently, not just hidden in the UI. I also think about rate limiting for sensitive endpoints like login and password reset, because those are common targets for abuse. When handling uploads, I validate file type, size, and storage location carefully to avoid dangerous files being executed. In reviews, I look for places where user input could reach HTML output, which means escaping is essential to prevent XSS. My overall approach is to assume user input is untrusted and to make secure defaults the easiest path for the team. Security is much easier to maintain when it is built into the design.
Question 9
Difficulty: easy
Describe a time when you disagreed with a teammate about a technical decision. How did you resolve it?
Sample answer
I think disagreements are healthy if they stay focused on the problem instead of becoming personal. In one project, we disagreed about whether to introduce a new abstraction layer for a set of PHP services. I felt the proposed design was too heavy for the current size of the codebase, while my teammate wanted stronger separation up front. Instead of arguing abstractly, I suggested we compare both options against real requirements: expected complexity, testability, and how likely the area was to change. We reviewed a few upcoming features and agreed that only part of the system needed the extra structure. We implemented a lighter design first, but left room to evolve it later if needed. That compromise gave us clarity without overcomplicating delivery. I’ve found that when people explain the tradeoffs clearly and keep the focus on the project goals, it’s usually possible to find a good middle ground. I try to be open, respectful, and evidence-driven in those conversations.
Question 10
Difficulty: easy
If you joined our team as a PHP Developer, how would you ramp up in the first few weeks?
Sample answer
My first priority would be understanding the product, the architecture, and the development workflow before trying to make big changes. I’d spend time reading the codebase, running the application locally, and learning how deployments, testing, and issue tracking work on the team. I’d also ask questions about the most important business flows, because understanding what matters to users helps me prioritize my effort. In the first few weeks, I’d aim to make a few small, safe contributions so I can get familiar with the standards and build trust with the team. That might include fixing minor bugs, improving tests, or cleaning up a focused area of code. I’d also pay attention to recurring pain points so I can identify where I can add value fastest. I like to ramp up in a way that balances curiosity with respect for the team’s existing process. That usually leads to better decisions and faster impact.
