PHP Code Review Checklist:
Security, Best Practices, and Tools

PHP allows for many ways to achieve the same outcome. Without a well-structured PHP code review, inexperienced developers can shortcut, ignore the separation of concerns, write inconsistent code, forget about security checks, or make other critical mistakes. These problems pile up as more engineers contribute to the application.

Our guide outlines how to run codebase reviews faster, more effectively, and repeatably without excessive micromanaging. It covers what to check, which tools to use, and how to automate your review cycles.

If you just need the essentials, here’s a quick checklist before diving into the full PHP code review process.

• Standards and readability: Enforce PSR-12 style, use declare(strict_types=1), choose clear, descriptive names, remove dead code.
• Syntax and language constructs: Use strict comparisons, braces on all control structures, avoid deprecated functions, no global state in functions.
• Functionality: Validate all inputs (including edge cases), ensure outputs match declared types, keep functions single-purpose.
• Error handling: Use specific exceptions, handle errors explicitly, avoid @ suppression, log with context.
• Security: Sanitize inputs/outputs, escape in templates, use parameterized queries, secure cookies, implement CSRF protection.
• ORM and database: Avoid N+1 queries, match models to schema, wrap multi-model updates in transactions, add down() methods to migrations.
• Dependency management: Lock versions, avoid wildcards/dev branches, keep composer.lock in sync.
• Performance optimization: Use efficient loops, paginate large queries, cache rarely-changing data, profile bottlenecks.
• Test coverage and quality: Cover critical paths and edge cases, enforce CI checks, ensure deterministic tests.

A PHP code review is a structured examination of PHP source code aimed at remedying bugs, clarifying logic, patching vulnerabilities, and enforcing strict style guidelines. For most businesses, routine assessments are the only practical way to scale development while meeting their objectives.

The main objectives of a PHP code review are to improve performance, protect against vulnerabilities, and maintain consistent coding standards. Code reviews give teams a way to catch and correct numerous errors and poor assumptions in a PHP codebase, which translates to multiple advantages:

• Improved performance before deployment. Systematic code reviews help detect wasteful loops, unoptimized database queries, inefficient scripts, and other poor design choices that slow the application. These problems can go unnoticed in small tests but cause major slowdowns when traffic increases. Catching these issues before deployment helps reduce response time, server load, and optimization costs.
• App reliability in all conditions. Reviewers assess how the app behaves during abnormally high demand or in rare conditions (bugs that appear when things happen incorrectly at high speed, like when several users change the same file at once). Regular checkups give developers more chances to test the logic, walk through decisions, and spot inconsistencies before code merging or release.
• Protection against security vulnerabilities. A PHP security code review checks if user input data (through forms, URLs, or cookies) is properly sanitized, which helps prevent SQL injections, cross-site scripting (XSS), and other malicious code. A comprehensive review also assesses whether the code reveals internal server error messages or external tools that can contain vulnerabilities.
• Clean and readable PHP code. Since PHP doesn’t force developers to write code in one way, the codebase can become a chaotic mess of inconsistent style and formatting. Companies that follow a PHP code review checklist and best practices will produce more consistent code that is easier to follow, test, debug, and improve.
• Reduced maintenance and technical debt. Shortcuts and sloppy code pile into problems that have to be fixed later. A thorough review process enables teams to spot these problems immediately and encourages them to think about the long-term consequences of their design decisions.
• Regular upskilling of PHP developers. In many companies, engineers must interpret bug reports, examine failed test logs, and resolve issues raised by quality assurance (QA) experts. Developers who act on consistent feedback write more maintainable and efficient code.

To achieve these objectives, it’s necessary to structure them. And a practical PHP quality and secure code review checklist can help with that.

Our checklist covers what well-reviewed PHP code should look like. We’ve drawn it up so you can use it for audits and to enforce standards across your projects.

PHP Coding Standards (PSR-12) and Readability

PHP allows a wide range of styles, but a lack of regulation can cause subtle bugs and miscommunications.

• Teams follow the PSR-12 formatting rules (the official PHP-FIG’s PSR standards), including 4-space indentation, opening braces on new lines, and mandatory declare(strict_types=1).
• Identifiers use descriptive names that reflect their role (e.g., $userEmail, getInvoiceTotal(), sendActivationEmail()) instead of vague variables and function names.
• Constants and configuration options are prioritized over magic numbers and strings (e.g., const SECONDS_PER_DAY = 86400;).
• Files contain exactly one class and a matching filename in StudlyCaps (e.g., UserProfileController.php).
• Private functions are split into smaller helpers that don’t exceed 50 lines.
• Formatters are enforced via pre-commit hooks or CI/CD checks to maintain consistent indentation and spacing across files.
• Commented-out and dead code blocks are removed when they are no longer needed to avoid noise during subsequent code reviews.

Syntax and Language Constructs

Syntax checks during a code review are critical to prevent runtime errors, avoid deprecated features, and keep the codebase maintainable for newer PHP versions.

• All functions and methods declare types for parameters and return values (e.g., function add(int $a, int $b): int).
• Braces wrap all control structures, even if if or for contains a single line.
• For switch statements, break, return, or throw follow each case to avoid accidental fall-through.
• Deprecated functions and syntax are disallowed; e.g., functions like each(), create_function(), split(), or mysql_* were removed after PHP 7.
• Arrow functions (fn($x) => $x * 2) are used for compact operations, while anonymous functions are reserved for multiline logic and control structures.
• Strict comparisons (=== and !==) enforce type and value checks over loose comparisons.
• Functions that rely on global state are banned inside other functions; the required data should come through parameters or constructor-injected dependencies.
• Constructs and patterns are simplified (e.g., patterns shouldn’t assign a value just to return it unless there’s a need to debug or reuse it).

Code Functionality

Functionality checks during code reviews ensure the code behaves as expected and handles input correctly.

• All supported inputs and edge cases are validated, including nulls, empty strings, Booleans, missing keys in arrays, and unexpected types.
• Outputs match documented return types and expectations (e.g., a function that declares : array should always return an array, even if it’s empty).
• Conditional branches have defined and deterministic outcomes (e.g., whether each if and else block behaves predictably).
• Pure functions return the same output for the same input unless they are documented as stateful (using timestamps, random values, external resources, etc.).
• Code shouldn’t crash or return cryptic errors; ensure it properly logs the error or raises a controlled exception.
• Network calls, filesystem access, and API integrations are protected with try-catch blocks and fallback paths.
• Boundaries and limits are thoroughly tested (e.g., zero, one, and maximum values).
• Each function should do one thing well (single-purpose functions) without mixing unrelated responsibilities into a single method.

Error Handling

Error handling strategy gives developers actionable diagnostics that can help prevent silent failures and analyze confusing output.

• Exceptions inherit from a base exception class (like AppException or DomainException).
• Only use try blocks to enclose operations that can fail to make it easier to understand which operations fail.
• Catch blocks handle errors explicitly (either logging, converting into a safe message, or rethrowing with additional context).
• Logged exceptions include the exception class name, message, and the request context, so the developers can reproduce and trace errors to the cause.
• Exceptions are caught at the correct boundary layer (e.g., application boundaries shouldn’t catch errors in business logic).
• Network requests have reasonable timeouts with retries or alternative flows; requests shouldn’t hang indefinitely.
• Logs have machine-readable fields (like timestamp, user_id, module, error_type, etc.) for easier searching and filtering.
• Global error handlers are banned unless justified (e.g., set_error_handler() or register_shutdown_function() would affect the whole runtime).
• Error responses match the request format (e.g., errors should return JSON if that’s the format that the API endpoint received).
• Users see user-friendly error pages, like 404 (not found) or 500 (server error), instead of white screens.

Security

A PHP code security review focuses on identifying vulnerabilities such as XSS, SQL injection, CSRF, and insecure session handling. To ensure the safety of the PHP code, a security review should treat all inputs, outputs, and interactions as potentially dangerous until verified otherwise.

• All user input is validated using functions like filter_input(), filter_var(), immutable custom classes (such as EmailAddress and PhoneNumber), or domain-specific value objects.
• User-supplied fields go through sanitization that neutralizes malicious input (e.g., removes JavaScript).
• Variables printed into a template are wrapped in htmlspecialchars() or an equivalent to prevent stored and reflected XSS.
• SQL queries are processed using parameterized statements (e.g., prepare() and execute()) to reduce the risk of SQL injection.
• Raw query templates and SQL with interpolated variables are rejected even if they appear sanitized.
• Actions that mutate server state require CSRF tokens that must be session-bound and verified before accepting the request.
• Session IDs are regenerated after login or role upgrade using session_regenerate_id(true).
• Secure, HttpOnly, and SameSite=Strict flags are set on cookies to prevent session theft through external sites.
• Authentication uses password_hash() and password_verify(); avoid MD5, SHA1, or plain hashing for passwords.
• File uploads are checked for type, extension, and size before saving.
• Error types are enabled in development and suppressed in production to prevent information leaks.
• Frontend messages in PHP apps don’t expose internals (traces, file paths, or class names in frontend responses).

For related performance considerations, see the Performance Optimization section below.

Object-Relational Mapping

Object-Relational Mapping (ORM) can introduce hidden queries, performance issues, or misuse of abstraction. Teams that use Doctrine, Eloquent, or Propel should review several aspects to keep the data layer maintainable and efficient.

• Models accurately reflect the database schema (database tables match the columns, data types, values, and key relationships in models or mapping files).
• Repeated model access inside loops should trigger a warning unless joined or prefetched to eliminate N + 1 query problems (executing one query per item plus the initial one).
• Post-query logic is encapsulated in custom collections (e.g., Eloquent allows overriding newCollection() to chain operations like $posts->published() to keep logic out of controllers).
• Builder classes are used for complex query logic on database classes (e.g., UserBuilder).
• Automatic type conversion aligns with the database schema and application logic (e.g., a custom class like Money in Laravel should implement correct behavior in both read and write operations).
• Operations that update multiple related models use explicit transactions (e.g., DB::transaction() or Doctrine’s TransactionManager).
• Every migration should have a corresponding down() method that cleanly reverts schema changes to ensure safe rollback.
• Caching mechanisms are used for datasets that rarely change (e.g., cache() in Laravel, Doctrine ResultCache, or Redis).

Dependency Management

During a code review, teams should check the installation, versioning, scope, and integration of dependencies.

• Production builds run composer install –no-dev –prefer-dist to avoid using test packages.
• composer.lock is committed and matches composer.json to avoid fetching wrong dependency versions.
• Semantic version constraints (^, ~) are used for safe updates without risking breaking changes.
• Wildcard (*), open-ended (>=1.0), or dev branch (dev-master) version constraints are rejected, as they can lead to unpredictable builds.
• Test-only libraries are placed under require-dev and never used in production.
• All packages are architecturally consistent with the rest of the PHP project.

For security-focused dependency checks, see the Security section.

Performance Optimization

A PHP performance review examines how the code handles large datasets, database queries, and memory usage under load. Teams take care of optimization as they review the PHP code to reduce server load and eliminate bottlenecks in high-traffic environments.

• For array traversal, foreach is prioritized over for to avoid repeated calls or pointer manipulation.
• Nested loops shouldn’t iterate over large datasets without exit conditions, as they hinder performance in nested queries or transformations.
• Unnecessary object creation or repetitive instantiation is flagged; reuse static values, constants, or cached instances if the object’s behavior doesn’t change.
• Native PHP functions are used for mapping, filtering, or sorting (e.g., array_map(), array_filter(), array_reduce(), and usort()).
• LIMIT is configured for clauses or pagination in all queries returning user-facing data.
• Modules and requests have a set baseline for acceptable response time, memory use, or DB query count.
• Cache-Control, ETag, or Last-Modified headers are set for static assets to avoid repeated downloads.
• Lazy loading with generators (yield), chunked iterators, or cursor-based fetching is used to stream large datasets without straining the application memory.
• Pull requests (PRs) include performance metrics (request time, memory usage, or rows affected) to assess the performance impact of changes.

For database-specific optimizations, review the Object-Relational Mapping (ORM) section above.

Test Coverage and Quality

A PHP source code review should evaluate whether tests check real behavior, use strong assertions, and cover meaningful edge cases.

• All critical business paths are explicitly tested with realistic inputs and expected results.
• The total code coverage threshold should be over 80% to catch regressions or drops.
• New code patches have at least one test per logical outcome (e.g., test not just valid, but also invalid cases for user input validation).
• Complex logic requires a corresponding test or testable stub; this includes functions with multiple branches and non-obvious logic.
• Tests use mocks for all external services in dependency tests.
• Each test is isolated and deterministic, meaning it should return the same result regardless of execution order or environment state.
• CI system runs tests on every commit and blocks merges on failure or skipped assertions.
• Slow tests that delay feedback are profiled for later optimization.
• Test cases have descriptive test names that reflect actual behavior (e.g., test_invoice_total_includes_tax_when_tax_flag_is_true()).

Even with a comprehensive checklist, you still need to plan your review process. 

Over the years, DevCom has audited hundreds of codebases across legacy rewrites, greenfield SaaS products, and enterprise systems. The following recommendations can help you accelerate your review process:

• Define goals before starting the PHP code review; without a clear focus, it may boil down to nitpicking and exchanging vague opinions.
• Write review scopes in PR descriptions to clarify what the team should check.
• Attach relevant specs or Jira tickets to the PR to further explain the purpose and requirements for the code.
• Separate non-critical commits from logic changes for reviewers to focus on the priority task.
• Rotate reviewers to distribute knowledge about the codebase across the team.
• Review composer scripts in composer.json to ensure safety; otherwise, these scripts can run shell commands that execute unnecessary operations or serve as backdoors.
• Conduct periodic code and dependency audits (with tools like composer outdated or composer show –latest) to identify unused libraries and outdated packages.
• Update the PHP code review checklist after every post-release bug to cover more issues in the next project.
• Public methods should have PHPDoc comment blocks that explain their purpose, expected input, return values, and possible exceptions.
• Inline comments should describe intent, edge case handling, or domain logic, rather than merely restating the code.
• Use data providers to test multiple inputs to increase visibility into edge cases without duplicating code.
• Encourage mutation testing tools that change your code to introduce minor faults, which help detect weak test cases.
• Clean up all generated files, sessions, and data after tests run using teardown methods or transaction rollbacks.
• Keep architecture decision records (ADRs) in a version-controlled folder with files outlining problems, solutions, and considered alternatives.
• Structure-affecting architectural and technical changes should trigger an ADR so future reviews will understand why changes happened and confirm they’re safe to modify.

Review tools can help you assess the code more easily and even automate several checks.

Effective PHP code reviews rely on a combination of quality analysis tools, security scanners, and automation utilities. A strong code review depends on reliable tools that can help your teams spot, identify, and remediate problems efficiently. We broke these into categories, though some overlap in roles.

➤ Code Quality Dashboards

Dashboards combine data from static analysis, test coverage, duplication detection, and other metrics.

• SonarQube aggregates data about bugs, code smells, security vulnerabilities, test coverage, duplicated code, complexity, and more.
• Code Climate analyzes the code to assign maintainability scores to different aspects of the code.

➤ Static Analysis and Linters

Static analysis tools scan PHP code without running it to help reviewers catch problems before they escalate into production.

• PHPStan is a configurable type-checker that catches mismatches, undefined variables or methods, invalid property access, and other semantic errors before runtime.
• Psalm offers deep type inference, undefined variable detection, and security-oriented analysis.
• PHP_CodeSniffer is a token-based tool that enforces coding styles such as PSR‑12 (or custom rules), highlights violations, and auto-corrects fixes.

➤ Security Scanners

Security scanners analyze how data flows through the application to uncover injection points, unsafe deserialization, or exposed credentials.

• SonarPHP (part of SonarQube) flags weak cryptography, input validation gaps, SQL injections, unsanitized input, insecure deserialization, and code smells.
• Exakat applies hundreds of security and design rules and generates in-depth reports about insecure logic.

➤ CI/CD and Automation Utilities

These code review tools for PHP codebases automate various checks during the audit and QA.

• GitHub Actions automates linting, scanning, and testing on pushes or pull requests.
• PHPUnit is a testing framework that validates logic, catches regressions, and confirms behavior (across classes, functions, and modules).
• Jenkins is a scriptable CI tool that you can extend for PHP tools like PHPUnit and PHPStan.

➤ Collaborative Review Platforms

These platforms help teams handle PRs, inline comments, diffs, reviewer assignments, merge checks, and policy enforcement.

• GitHub’s pull request and merge request tools help track comments, status checks, review approvals, and gate merges using branch protection rules.
• Bitbucket’s Code Insights adds annotations for test results and static analysis directly into the diff view.

Even experienced teams can overlook simple errors, especially if they’re working under pressure. 

These mistakes show up even in senior teams, especially if reviews happen under pressure. Keeping this table next to your code review checklist can prevent common problems.

If you’re catching the same minor issues repeatedly, it may signal that your process needs more automation.

Automation removes the repetitive, error-prone, and time-consuming parts of code review. Of course, it only helps when reviewers shift focus to deeper business logic, structure, and architecture.

Below are practical ways to automate PHP code reviews used by mature development teams.

• Run static analysis tools in commit hooks. Static tools like PHPStan and Psalm in Git pre‑commit or CI/CD pipelines help spot undefined properties, incorrect method calls, missing type hints, and other code errors.
• Enforce PSR standards. Use PHP_CodeSniffer or similar tools to enforce PSR-12 in indentation, brace style, line length, and naming conventions.
• Gate PRs with CI/CD checkpoints. GitHub Actions, GitLab CI, or Jenkins can run various tests at each PR, with coverage thresholds that block merges if tests fail or analyzers report errors.
• Enable auto-merge when all checks pass. Allow PRs to merge automatically when all automated checks pass and a senior or designated reviewer approves.
• Push code review stats to the team chats. Tools like Reviewpad and CodeScene can help push metrics about slowdowns or neglected areas to Slack or other chat platforms.
• Automate dependency updates. Dependabot or similar tools can monitor dependency files (composer.json/composer.lock) and create PRs with changelogs and compatibility notes if libraries issue updates.
• Run scheduled scans. SonarQube can analyze the codebase during off-hours, delivering reports on code duplication, complexity hotspots, security issues, and signs of technical debt.

DevCom provides PHP code review services that go beyond surface-level checks. Our professionals combine static analyzers, manual walkthroughs, and runtime checks to flag all inconsistencies.

Our team can audit your source code to identify bottlenecks and scalability issues. We can also work closely with your developers and CI/CD pipelines to catch technical debt, anti-patterns, or undocumented behavior as code is written, gradually reducing technical debt.

Certified AWS and Azure engineers can review how your PHP application runs in production. This includes inspecting Dockerfiles, Kubernetes manifests, database connection patterns, and the runtime performance of serverless PHP functions.

Planning a refactor, cleaning up legacy code, or trying to reduce security risk? Contact us to learn how we can help you improve your codebase.