The Symfony PHP framework is a strong choice when building web applications that demand stability and scalability. but to fully unlock its potential, Symfony developers need to stick to best practices that boost code quality and security. This article shows how to use PHP Symfony effectively—and how to dodge the usual pitfalls.
#1 Always go with the latest Symfony LTS release
It doesn’t matter whether you’re coding a company portfolio site or a sprawling e-commerce app, always pick the latest long-term support (LTS) version. LTS means a version of Symfony that gets extended maintenance.
How it works
Symfony follows a release cycle with versions X.0, X.1, X.2, X.3, and X.4. the X.4 version is the one labeled LTS.
Why does LTS matter?
Non-LTS versions get support for just six to eight months. After that, you’re on your own. in contrast, LTS releases come with two years of bug fixes and an extra year of security patches. Sometimes that support window gets extended—like with version 5.4, released in November 2021. Thanks to its popularity, security updates were extended all the way to February 2029. That’s over seven years of peace of mind.
When the client wants bleeding-edge features
Sometimes a client insists on using features available only in the latest non-LTS version—features not yet in the current LTS. What then?
Start with the roadmap
Before making a call, check Symfony’s official release calendar. If your project timeline overlaps with the release of the next LTS, you might consider using a non-LTS version, but only after flagging these critical caveats:
- Non-LTS versions can be unstable. Be transparent with the client.
- They may contain unpatched security vulnerabilities. Invest more in penetration testing.
- They require regular updates. That means time to adjust the code if needed.
- Maintenance matters. Your app reflects on you as a dev and on your team. Let the client know that once the LTS drops, you’ll need to update the app and monitor it—especially for patch versions in the first month (check out the description of semantic versioning). After that, a twice-yearly package update usually suffices.
What if you skip LTS?
In the short term, nothing dramatic. but if your strategy is “build and forget,” sure, go with a non-LTS version. Just ask yourself: is that the kind of dev you want to be?
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Let’s talk updates
Imagine a security flaw lets users gain admin access through a crafted request. Nightmare scenario. Now you need to patch fast. Two apps, same architecture: frontend for users, backend for admins.
- App 1 runs on Symfony 5.1.
- App 2 runs on Symfony 5.4 LTS.
Updating App 1 (non-LTS):
Support for 5.1 ended in January 2021. No security patches since. Here’s the drill:
- Run unit tests to catch deprecated code with PHPUnit.
- Fix the deprecations.
- Update composer.json to 5.2 (step through minor versions).
- Run composer update “symfony/*”.
- Update other packages if they break compatibility.
- Repeat steps 1–5 until you hit version 5.4.
That’s a lot. and step 4 might break libraries in ways that force major rewrites. a “minor” patch turns into a big overhaul.
Updating App 2 (LTS):
Bug fixes for 5.4 ended in November 2024, but security support runs until February 2029. What do you do?
- Run composer update “symfony/*”.
- Run unit tests to check for deprecations.
- Fix them.
- Optionally, update other libraries.
Way less work. and if your app’s already maintained regularly, you might just need steps 1 and 2. Clean. Quick. Safe.
#2 Test your code
Code without testing is broken by design.
That’s not just a catchy phrase, it’s a quote from Jacob Kaplan-Moss, cocreator of the Django framework. and it rings true across all languages and frameworks, Symfony included.
Why testing matters
Bugs don’t always stem from sloppy coding. Often, they sneak in during library updates. If a library starts behaving differently after an update and no one’s watching, things break—quietly.
The two kinds of bugs
When you hear “bug,” you probably think syntax—missing semicolons, dangling braces. but syntax errors are rare, especially with experienced developers. Functional bugs are far trickier. Two common scenarios:
- Misunderstood or missing documentation. Developers tend to simplify tasks. If the workflow is complex and under-documented, some paths get skipped. the result? Code that works—until it doesn’t, when real-world data hits.
- Dependency updates. Reusing libraries is smart. but when you bump a major version (hello semantic versioning), you risk breaking things. Say the rounding behavior in a tax library changes. That’s a minor tweak with major implications for your invoicing module.
How do you test?
There’s no universal answer. Two common strategies:
1. Test-driven development (TDD): Write tests first, code later. Benefits include:
- verified functional requirements;
- higher test coverage;
- fewer regressions.
But it’s slow and demands strong documentation, which isn’t always available.
2. Post-implementation tests: Faster to code, but riskier. Developers might bend the test to fit the code, not the other way around. Edge cases often slip through.
And then there are projects with no tests at all. Taking one over from another team? You’re walking into a minefield.
When to run tests
- After each code change. Whether tests come before or after the feature, run them.
- Before pushing code. Use a Git hook to catch issues early.
- In the CI/CD pipeline. Failed tests should block merges and deployments.
Don’t let test coverage drop
Say your app has 92% test coverage. You add a new feature, but your branch drops that to 88%. Two possibilities:
- You didn’t write tests for the new code.
- You removed obsolete tests.
While the first case is unacceptable and should completely disqualify the pull request, in the second case, the person performing code review should carefully analyze the task. It’s possible that the tested functionality has changed or been removed, making the tests obsolete. in such a situation, the change should not disqualify the pull request.
What if there are no tests?
Maybe nothing happens. Maybe everything breaks.
Take a microservice that generates invoices. it uses a payment gateway SDK and a tax calculation library. One day, you update both. Without tests, you eyeball things locally and push to staging, and a week later QA reports that VAT is being miscalculated. it turns out that the tax library changed how it rounds numbers in its latest major version. it took hours to track it down.
That was a lucky scenario. We’ve all seen worse: untested code dumped straight to production.
With tests, though?
Say you had a test that checked VAT totals. That rounding bug would trigger a failure during development. You’d catch it early, fix it fast, and deploy with confidence.
Tests aren’t just insurance—they’re a speed boost for every future change.
#3 Use static code analysis and code style tools
The more developers on a project, the harder it is to keep the code clean and consistent. Everyone has their own coding style, and without discipline, your codebase can turn into chaos. Refactoring becomes a nightmare.
My go-to tools: PHPStan and PHP CS Fixer. Simple, powerful, essential.
What is static code analysis?
Static code analysis inspects your code without running it. it flags errors, security issues, and coding standard violations early, before your tests even start. Unlike dynamic analysis, it focuses on code structure and syntax. This means you catch issues long before they hit production.
Why use static analysis?
- Catch bugs early. Tools like PHPStan analyze types and structure, warning you about issues as you code.
- Cleaner, faster code. Good code isn’t just readable, it’s efficient. Static tools help eliminate wasteful operations and boost performance.
- Lower cost, higher quality. Fixing bugs during development is cheaper than fixing them later. Less rework means happier clients. Happy clients come back—and they tell their friends.
- Easier teamwork. These tools accelerate code reviews. Run them in your CI/CD pipeline to block bad code before it merges. it saves review time and minimizes human error—even the best devs miss things.
What about code style tools?
Code style tools, “fixers” such as PHP CS Fixer, enforce consistent formatting. Whether you’re following PSR-1, PSR-2, or a custom style, these tools automatically clean up your code.
They can:
- modernize syntax (e.g., convert pow() to ** in PHP 5.6+);
- optimize redundant logic; and
- enforce consistency across teams and projects.
Unlike linters, which only detect issues, fixers actually fix them.
Why bother?
- They do the dirty work for you. Fixers spot outdated or messy code and clean it up automatically—no more worrying about deprecated features.
- They unify team standards. Ever had a pull request rejected for formatting? or had to learn new styles at a new company? These tools remove that friction. Agree on the rules, enforce them project-wide, and make onboarding new devs a breeze.
Solo devs, take note
You might think: “Why bother if I’m the only developer?” but your code might come back to you in six months—or six years. Poor-quality code is a pain to revisit.
And projects often move from one team to another. Without a shared set of standards, that handover gets messy fast. If the project eventually comes back to you, its condition will depend entirely on how well you prepared it in the first place.
Write code your future self will thank you for. Use static analysis. Enforce style. Keep it clean.
#4 Use type declarations and enforce type checking
With PHP 7.0, the language got a major upgrade—a true game changer compared to version 5.6. Native type declarations were added, replacing the old-school annotations that were basically just glorified hints. Suddenly, you could define argument and return types directly in your functions.
- PHP 7.0 – Introduced function and return type declarations.
- PHP 7.1 – Added nullable, void, and iterable types.
- PHP 7.2 – Introduced the object type.
- PHP 7.4 – Brought type declarations to class properties.
- PHP 8.0 – Introduced union and mixed types.
- PHP 8.1 – Added the never type.
- PHP 8.2 – Allowed null and false as stand-alone types; introduced the true literal type.
- PHP 8.3 – Brought type declarations for class constants.
These features dramatically improved developer experience. and yet, PHP stayed true to one principle: Variables don’t have types—values do.
What’s type enforcement?
By default, PHP doesn’t require you to declare types. but doing so makes your code safer and easier to debug. Let’s look at a simple example:
<?php
function addTwo($x) {
return $x + 2;
}
echo addTwo(3.14);
We see a function that’s supposed to work with integers (it’s meant to add two to them). but we enter 3.14, a float number! Still, PHP processes the operation and prints the result: 5.14.
Let’s tweak the code a bit and add type declarations:
<?php
function addTwo(int $x): int {
return $x + 2;
}
echo addTwo(3.14);
Now our function clearly states it expects an integer as input and will return an integer. and here’s where the trouble begins.
PHP sees the return type int and performs an implicit type conversion. as a result, we lose part of the data. on top of that, PHP throws a syntax error. the outcome looks like this:
Deprecated: Implicit conversion from float 3.14 to int loses precision in /app/public/test.php on line 3
5
And now, the final change: We enforce strict typing by adding the line declare(strict_types=1);
The code now looks like this:
<?php
declare(strict_types=1);
function addTwo(int $x): int {
return $x + 2;
}
echo addTwo(3.14);
At this point, your IDE should already flag an error—see Figure 1 below:
Fig.1. Type error warning displayed in PHPStorm.
Additionally, the script will fail to execute properly. in the browser, we’ll get the following result:
Fatal error: Uncaught TypeError: addTwo(): Argument #1 ($x) must be of type int, float given, called in /app/public/test.php on line 11 and defined in /app/public/test.php:5 Stack trace: #0 /app/public/test.php(11): addTwo(3.14) #1 {main} thrown in /app/public/test.php on line 5
At this point, you might wonder: How are types actually helping us? the example clearly showed that without typing, we got a valid result—yet once we added types, the program suddenly stopped working the way we expected.
The answer is simple: typing gives us control, and that control is crucial.
In the Symfony framework, we frequently work with databases. If you’re using Doctrine ORM, you’re dealing with entity classes that map directly to database tables. as we know, an entity is a representation of a table in a relational database. and database tables have columns—each with a defined data type.
Now, imagine this scenario:
You don’t use type declarations
Your entity class might look like this:
<?php
namespace App\Entity;
use Doctrine\ORM\Mapping as ORM;
#[ORM\Entity]
class MyEntity
{
#[ORM\Id]
#[ORM\GeneratedValue]
#[ORM\Column(type: 'integer')]
private $id;
#[ORM\Column(type: 'integer')]
private $myValue;
public function getId()
{
return $this->id;
}
public function getMyValue()
{
return $this->myValue;
}
public function setMyValue($myValue)
{
$this->myValue = $myValue;
}
}
As you can see, the only data-type enforcement happens at the database level. This means our code can pass any value to the $myValue field. What could that lead to? a 500 Internal Server Error when trying to save invalid data.
And to trace that error, we’d have to inspect the database connection. That’s way too late in the process to be catching bugs.
Let’s explore a better approach.
You use type declarations, but without strict type enforcement
In this case, your entity class looks like this:
<?php
namespace App\Entity;
use Doctrine\ORM\Mapping as ORM;
#[ORM\Entity]
class MyEntity
{
#[ORM\Id]
#[ORM\GeneratedValue]
#[ORM\Column]
private ?int $id;
#[ORM\Column]
private int $myValue;
public function getId(): int
{
return $this->id;
}
public function getMyValue(): int
{
return $this->myValue;
}
public function setMyValue(int $myValue): void
{
$this->myValue = $myValue;
}
}
As you can see, the only data type enforcement happens at the database level. This means our code can pass any value to the $myValue field. What could that lead to? a 500 Internal Server Error when trying to save invalid data.
And to trace that error, we’d have to inspect the database connection. That’s way too late in the process to be catching bugs.
Let’s explore a better approach.
You use type declarations, but with strict type enforcement
In this case, your entity class looks like this:
<?php
declare(strict_types=1);
namespace App\Entity;
use Doctrine\ORM\Mapping as ORM;
#[ORM\Entity]
class MyEntity
{
#[ORM\Id]
#[ORM\GeneratedValue]
#[ORM\Column]
private ?int $id;
#[ORM\Column]
private int $myValue;
public function getId(): int
{
return $this->id;
}
public function getMyValue(): int
{
return $this->myValue;
}
public function setMyValue(int $myValue): void
{
$this->myValue = $myValue;
}
}
The code snippet above is a more complex example. the IDE will already warn us about the incorrect data type—and if we still miss the alert, the application will throw a 500 error when it encounters invalid data.
What happens if you don’t enforce types?
Let’s take our simple examples and apply them to a real-world case. Say you’re building an e-commerce system. at the core of e-commerce are products, and every product needs a price (whether it’s stored in the product model directly or in a related model doesn’t matter).
The safest way to store a product price? as an integer—meaning in cents. Why? Because integers behave more reliably during operations like calculating discounts. but that’s a topic for another day.
Now imagine multiple developers working on the project. the team doesn’t enforce strict type control. One dev creates the product model (an entity), adds type declarations, and writes a setter for the price that expects an integer. Another dev builds the admin panel. Naturally, though, it’s easier for humans to enter prices in dollars and cents (e.g., 123.00), and this second developer assumes—based on experience from another company—that the price is stored as a decimal in the database. So they don’t convert dollars to cents.
The code goes through review. No one catches the mistake.
Once deployed to the test environment, a serious issue appears. the admin enters a price of 123.00 USD. on the frontend, it shows up as 1.23 USD.
What happened? the setter stripped the decimal part and saved 123 to the database—123 cents. the frontend displays that as dollars, giving us 1.23 USD.
This could’ve been avoided with proper type control. a strict-typed setter would have immediately thrown an error, alerting the dev before anything made it to staging.
#5 Don’t reinvent the wheel—use proven libraries
This seems obvious. and yet, in countless legacy projects, custom solutions to well-known problems are everywhere.
Why does this happen?
Many junior developers want to prove their skills. They build custom systems—not for complex business logic, but for things that already have polished, open-source solutions. They write hundreds of lines of code that could be replaced with a library and one clean line.
Why is this a problem?
Community-backed libraries are tested, maintained, and optimized by more people than any one dev could ever match. If the library is widely adopted and actively maintained, you can bet it’s more efficient than your homegrown version.
And there’s the update problem. APIs change. If you’ve built your own integration, you might need to rewrite large chunks of code. but with a proper library, backward compatibility is often guaranteed. Sometimes the only thing you need to do is update the package. That’s convenience you can’t ignore.
What other risks come from not using libraries?
Let’s look at a common example—something nearly every application needs: password reset functionality.
Here’s the typical flow:
- The user clicks “Forgot password.”
- They enter their email address.
- The system sends an email with a reset link.
- The user sets a new password.
Sounds simple—but there’s a lot that can go wrong:
- You must avoid revealing whether an account exists for a given email (return a success message either way).
- The reset link must be unique.
- The link must expire after a set time.
- The reset token should not appear in the URL (store it in a session and redirect instead).
- You must rate-limit reset requests per user over time.
And the list could go on.
What seems like a basic feature quickly becomes a security minefield. Luckily, there are libraries for that—like SymfonyCasts/ResetPasswordBundle.
Should you be cautious with libraries?
Absolutely.
- Read the license. Before adding any library, check its license carefully. You don’t want to unintentionally turn your commercial product into free software because the library forces open-source redistribution.
- Check popularity. on repositories like Packagist, look at install counts. More installs usually mean more community trust.
- Review issues and vulnerabilities. a popular library with lots of unresolved bugs or security issues? Red flag.
And if you skip the library?
You’re making life harder—for yourself and every dev who follows you.
Here’s a real-world example: implementing a payment system for an online store. the client chooses payment gateway XYZ, which offers a PHP SDK and full REST API documentation. Instead of using the SDK, you decide to write your own integration from scratch using raw API calls.
The app launches. the client is happy.
Six months later, the phone rings: “Hey, it’s not working. What did you sell me?”
You investigate. It’s a 500 error. Turns out, the API changed. the request and response structures are completely different.
Now you’re rewriting the entire integration. Several hours of work—gone.
Had you used the SDK? You’d probably just update the library version. Done in minutes.
Sure, the example is extreme—no payment gateway would introduce breaking changes to its API within just six months. However, similar situations can be found in other types of applications as well.
Use libraries. They exist for a reason.
Symfony development best practices—summary
Building web applications or creating complex websites with Symfony PHP takes more than just knowing the framework. You need to master Symfony best practices that ensure code quality, security, and long-term maintainability.
Using LTS versions, writing tests, running static analyses, enforcing strong typing, and leveraging existing libraries all help minimize bugs and speed up development. Ignoring these principles can lead to costly updates, performance hits, and growing maintenance overheads.
And one more thing: Always follow the official Symfony documentation, especially the Best Practices section. it exists for a reason: to help you discover Symfony ecosystem.
