Interview Questions to Hire the Right PHP Developer

• McKinsey & Company: Firms in the top quartile of Developer Velocity achieve 4–5x faster revenue growth than peers in the bottom quartile, linking elite engineering talent to business outcomes.
• Statista: Roughly three‑quarters of websites with known server‑side technology run on PHP, underscoring the continued need for strong PHP hiring practices.

Which core PHP fundamentals should you verify during screening?

You should verify core PHP fundamentals during screening by assessing language constructs, execution model, and error handling to reduce risk with php developer interview questions.

• Prioritize PHP 8+ features (typed properties, union types, attributes, match) and comfort with strict types.
• Confirm array mastery, references, SPL, and superglobals with lifecycle awareness across requests.
• Check Composer basics, PSR‑4 autoloading, and semantic versioning for dependency hygiene.
• Validate FPM vs CLI behavior, opcode caching, and configuration boundaries via php.ini.
• Probe error/exception taxonomy, type errors, and custom handlers for resilience.
• Tie fundamentals to maintainability, observability, and predictable runtime behavior.

1. Types, arrays, and references

• Scalar and composite types in PHP 8+ with strict typing and nullable signatures.
• Arrays as ordered maps, iterators, generators, and memory traits across versions.
• Type safety reduces defects, clarifies contracts, and simplifies refactoring cadence.
• Efficient array usage improves CPU cache locality, I/O patterns, and memory headroom.
• Adopt strict_types, typed properties, and return types in greenfield and refactors.
• Use iterators, array_* ops, and references deliberately within profiling feedback.

2. Namespaces, autoloading, and Composer

• PSR‑4 namespaces enforce modular structure and predictable class resolution.
• Composer orchestrates dependencies, scripts, classmaps, and lockfile integrity.
• Clear module boundaries curb coupling, speed onboarding, and enable parallel work.
• Reproducible builds prevent drift, reduce incidents, and stabilize deployments.
• Define autoload rules, prefer library splits, and pin constraints with caret ranges.
• Vendor audit, composer validate, and security advisories govern upgrades safely.

3. Runtime, configuration, and error handling

• FPM worker pools, CLI context, and opcache dictate execution throughput.
• Error levels, exceptions, and logging sinks shape failure visibility and control.
• Tuned pools limit tail latency, improve saturation, and enhance fairness under load.
• Structured errors accelerate triage, root cause isolation, and postmortem quality.
• Right‑size pm settings, align opcache with code volume, and segregate configs.
• Normalize exception classes, centralize handlers, and stream JSON logs to APM.

Get a tailored PHP screening rubric mapped to your stack

Can you assess object-oriented design proficiency in PHP effectively?

You can assess object-oriented design proficiency in PHP effectively by probing SOLID usage, interfaces, and dependency injection through scenario‑based prompts.

• Start with refactor prompts, boundary seams, and contract‑first reasoning.
• Use change stories to reveal coupling, cohesion, and interface clarity.
• Validate testability through seam creation and DI container ergonomics.
• Examine tradeoffs among inheritance, traits, and composition in practice.
• Inspect domain modeling quality with value objects and aggregates.
• Align findings to maintainability, extensibility, and defect containment.

1. SOLID principles in PHP

• Single responsibility, open‑closed design, and interface segregation in codebases.
• Liskov substitution and dependency inversion across service layers and modules.
• Disciplined design curbs ripple effects, supports extensions, and limits regressions.
• Clear contracts reduce ambiguity, accelerate reviews, and stabilize release trains.
• Encapsulate variations, use policies, and prefer composition over inheritance.
• Enforce interfaces, small classes, and CI checks for cyclic dependency control.

2. Interfaces, traits, and abstract classes

• Interfaces define contracts; traits share behavior; abstract classes guide families.
• Each mechanism targets distinct reuse and polymorphism needs within domains.
• Appropriate selection reduces complexity, ambiguity, and diamond‑shape risks.
• Contract clarity accelerates swaps, mocks, and upgrade cadence across teams.
• Choose interfaces for capabilities, traits for mixins, abstracts for skeletal logic.
• Limit trait side effects, document precedence, and favor explicit composition.

3. Dependency injection and inversion of control

• DI moves construction to containers; IoC centralizes lifecycle and wiring.
• Service locators, factories, and containers mediate bindings and scopes.
• Decoupled wiring streamlines tests, fosters plugability, and eases upgrades.
• Clear seams enable mocking, contract validation, and latency isolation.
• Register services, use typed hints, and emit configuration per environment.
• Prefer constructor injection, minimal globals, and strict container validation.

Schedule a role‑aligned PHP design deep‑dive with senior assessors

Are framework-specific skills in Laravel or Symfony essential for your role?

Framework-specific skills in Laravel or Symfony are essential when the codebase relies on their conventions, tooling, and ecosystem components.

• Map daily tasks to routing, ORM, queues, cache, and HTTP middleware usage.
• Validate artisan or console tooling habits for scaffolding and maintenance.
• Inspect environment config, secrets, and deployment friendliness.
• Align logging, events, and observers with production observability needs.
• Confirm package choices, long‑term support, and upgrade strategies.
• Ensure familiarity with testing harnesses and container binding patterns.

1. Routing, controllers, and middleware

• Route definitions, parameter binding, and controller orchestration patterns.
• Middleware pipelines for auth, rate limiting, and content negotiation duties.
• Clean routing yields predictable endpoints, stable contracts, and simpler docs.
• Middleware discipline centralizes cross‑cutting concerns and consistency.
• Define named routes, DTO inputs, and slim controllers with services.
• Compose middleware order, test edge cases, and monitor via request IDs.

2. Eloquent ORM vs Doctrine ORM trade-offs

• Eloquent favors active record ergonomics; Doctrine advances rich domain models.
• Loading strategies, relationships, and unit‑of‑work semantics differ materially.
• Picking the right ORM reduces query bloat, N+1 risk, and migration pain.
• Domain alignment improves readability, testability, and performance tuning.
• Use eager loading, scopes, and casting in Eloquent for clarity and speed.
• Apply repositories, value objects, and transactions with Doctrine precision.

3. Queues, jobs, and events

• Asynchronous jobs, event dispatching, and bus patterns in frameworks.
• Drivers span Redis, SQS, and RabbitMQ with retry and backoff controls.
• Offloading tasks trims p95 latency, protects UX, and raises throughput.
• Durable messaging supports resilience, recovery, and peak smoothing.
• Define idempotent handlers, structured payloads, and dead‑letter policies.
• Track job metrics, alert on retries, and audit failures in centralized logs.

Validate framework depth with hands‑on scenario assessments

Should database and query optimization expertise be part of php technical interview questions?

Database and query optimization expertise should be part of php technical interview questions because data access dominates latency and cost.

• Focus on indexing, cardinality, and execution plan literacy.
• Probe transactions, isolation, and deadlock avoidance strategies.
• Validate ORM query hygiene and pagination behavior under load.
• Examine caching tiers, invalidation, and consistency expectations.
• Check migration discipline, backups, and rollback preparedness.
• Tie choices to SLOs, cost ceilings, and compliance constraints.

1. SQL indexing and query plans

• B‑tree indexing, composite keys, and covering index design strategies.
• EXPLAIN plans, join order, and filter selectivity across queries.
• Proper indexes cut I/O, reduce CPU churn, and stabilize tail latency.
• Plan literacy prevents accidental scans, lock storms, and budget waste.
• Profile queries, align keys to predicates, and prune unused indexes.
• Track regressions, baseline plans, and gate changes with tests.

2. Transactions and isolation in MySQL/PostgreSQL

• ACID guarantees with isolation levels across engines and workloads.
• Locking behavior, phantom reads, and conflict resolution patterns.
• Correct settings protect integrity, money flows, and audit trails.
• Predictable behavior reduces incident windows and customer impact.
• Choose levels per use case, segment hot rows, and shorten transactions.
• Add retries, idempotency keys, and circuit limits for safety.

3. Caching layers and pagination patterns

• Application caches, HTTP caching, and database‑adjacent stores.
• Offset vs keyset pagination with stability and performance tradeoffs.
• Smart caching trims compute, bandwidth, and database pressure.
• Stable pagination preserves ordering, UX, and replica health.
• Use cache tags, TTLs, and stampede protection with backfills.
• Favor keyset pagination for large sets; expose stable cursors.

Benchmark database depth with a targeted performance drill

Do your php screening questions cover HTTP, APIs, and security controls?

Your php screening questions should cover HTTP semantics, API contracts, and security controls to safeguard data and uptime.

• Validate HTTP methods, status codes, and content negotiation principles.
• Confirm OpenAPI discipline, versioning, and idempotency practices.
• Probe authN, authZ, sessions, and token storage decisions.
• Check input handling, output encoding, and templating boundaries.
• Include CSRF, SSRF, XXE, and dependency risk prompts.
• Align answers to least privilege, observability, and recovery plans.

1. HTTP methods, status codes, and content negotiation

• REST verbs, safe vs idempotent actions, and cache directives.
• Media types, language negotiation, and error envelope standards.
• Correct semantics reduce ambiguity, breakage, and client churn.
• Predictable responses strengthen SDKs, docs, and partner trust.
• Enforce method discipline, clear codes, and consistent problem details.
• Leverage ETags, conditional requests, and sensible cache lifetimes.

2. Authentication, authorization, and session management

• Cookies, JWTs, opaque tokens, and state handling across tiers.
• RBAC, ABAC, and scope models for granular resource control.
• Robust identity flows defend accounts, data access, and audits.
• Granular rules reduce blast radius and privilege creep over time.
• Store secrets safely, set cookie flags, and rotate signing keys.
• Centralize policy checks, log decisions, and monitor anomalies.

3. Input validation, output encoding, and CSRF/XXE mitigation

• Validation libraries, schema contracts, and encoder placement rules.
• Templating contexts, CSP, and protections against common pitfalls.
• Early validation shrinks attack surface and simplifies control flow.
• Correct encoding blocks injection, leaks, and rendering issues.
• Apply allowlists, sanitize consistently, and separate concerns cleanly.
• Use CSRF tokens, disable external entities, and scan dependencies.

Run a security‑first API review with experienced PHP leads

Is testing, CI/CD, and code quality rigor non-negotiable for this hire?

Testing, CI/CD, and code quality rigor are non-negotiable for this hire to sustain delivery speed and reliability.

• Demand PHPUnit fluency, mocks, fakes, and deterministic suites.
• Require static analysis, PSR standards, and pre‑commit hygiene.
• Confirm CI pipelines, artifacts, and environment parity readiness.
• Inspect rollout strategies, canaries, and rollback muscle memory.
• Tie practices to SLOs, MTTR, and change failure rate targets.
• Reinforce quality gates linked to risk and business impact.

1. PHPUnit and test pyramids

• Unit, component, integration, and end‑to‑end layering strategies.
• Fixtures, doubles, and hermetic tests to stabilize feedback loops.
• Balanced layers speed iteration, cut flakiness, and raise confidence.
• Good feedback drives safer refactors and bolder, faster releases.
• Enforce fast units, targeted integrations, and slim end‑to‑end flows.
• Gate merges on coverage quality, mutation scores, and flake budgets.

2. Static analysis, linters, and PSR standards

• PHPStan or Psalm, PHP_CodeSniffer, and PSR‑12, PSR‑4 compliance.
• Type inference, dead code flags, and consistent style enforcement.
• Consistency reduces cognitive load and review friction across teams.
• Early findings limit defects, incidents, and toil in production.
• Tune rule levels, baseline debt, and fail builds on critical issues.
• Auto‑fix style, document deviations, and track debt burn‑down.

3. Pipelines, environments, and release strategies

• CI workflows, artifact promotion, and immutable delivery pipelines.
• Blue‑green, canary, and feature flag strategies across clusters.
• Reproducibility safeguards uptime, compliance, and audit needs.
• Progressive delivery limits risk while sustaining cadence.
• Template pipelines, codify infra, and isolate secrets by scope.
• Monitor releases, watch error budgets, and trigger rollbacks quickly.

Spin up a CI‑ready PHP hiring loop with measurable quality gates

Faqs

1. Which core PHP areas should interviewers prioritize first?

• Start with language constructs, type system, error handling, and Composer-driven autoloading to confirm foundational readiness.

2. How many php developer interview questions are enough for a 60‑minute screen?

• Plan 8–12 targeted prompts plus one short code task, reserving time for follow‑ups and tradeoff reasoning.

3. Should Laravel or Symfony expertise outweigh core PHP skills?

• Balance both; enforce strong PHP fundamentals, then confirm framework fluency aligned to your production stack.

4. Do php technical interview questions need database depth?

• Yes; indexing, query plans, transactions, and caching influence performance, cost, and data integrity.

5. Are take‑home assignments still useful for PHP roles?

• Yes when tightly scoped; pair with a live review to evaluate decisions, testing, and maintainability.

6. Can php screening questions fairly assess security competence?

• Yes; include prompts on input handling, output encoding, session safety, CSRF, and secrets management.

7. Which signals indicate senior‑level PHP engineering maturity?

• Clear tradeoffs, domain modeling, test design, incident narratives, and ownership of release quality.

8. What is the best way to validate culture and collaboration fit?

• Explore PR etiquette, code review habits, documentation patterns, and conflict resolution examples.

Sources

• https://www.mckinsey.com/capabilities/mckinsey-digital/our-insights/developer-velocity-how-software-excellence-fuels-business-performance
• https://www.statista.com/statistics/873915/worldwide-popularity-server-side-programming-languages/
• https://www2.deloitte.com/us/en/insights/focus/technology-and-the-future-of-work/it-talent-technology-hiring.html