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SOLID is a set of five design heuristics for making object-oriented code easier to change and reason about: Single Responsibility, Open/Closed, Liskov Substitution, Interface Segregation, and Dependency Inversion. In Laravel, apply them by keeping classes cohesive, introducing contracts where a real substitution boundary exists, and using the service container to assemble dependencies—not by adding an interface or service class for everything.
This guide uses Laravel 13.x documentation as accessed on September 29, 2026. The principles are useful prompts for design decisions, not a quality score or a guarantee of better outcomes. The SOLID principle definitions are commonly attributed to Robert C. Martin.
How do I apply SOLID principles in Laravel?
Start with the change you need to make. Ask what part of the system should own that change, what assumptions callers make, and whether a stable boundary would let you change an implementation without rewriting application policy. Then choose the simplest design that contains the change.
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Laravel’s service container can construct many classes automatically, and inject dependencies into controllers, middleware, listeners, and queued-job handlers. Interfaces generally need an explicit binding to the concrete implementation Laravel should provide. Dependency injection is the mechanism for supplying an object; dependency inversion is the design choice to keep higher-level policy from depending directly on low-level details.
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- Change locality: Would a new requirement force edits across unrelated classes?
- Coupling: Is business policy tied directly to a vendor or framework detail?
- Substitution: Can another implementation honor the same behavioral expectations?
- Scope: Does each client depend only on the operations it uses?
- Complexity: Does a proposed abstraction solve a current or credible need?
Laravel documents constructor injection and explains that concrete dependencies can often be auto-resolved without configuration. See the Laravel 13.x service container documentation. The definitions below are summarized in Baeldung’s SOLID overview; examples are illustrative teaching examples, not tested application code.
1. Single Responsibility: keep a class cohesive
The Single Responsibility Principle (SRP) says a class should have one responsibility—in the cited formulation, one part of a specification should be able to affect that class. It does not mean every method needs a separate class or that every multi-method class is wrong. Look instead for unrelated reasons a class changes.
A Laravel example
A controller can translate an HTTP request into an application call and turn the result into an HTTP response. A use-case class can own the coherent application operation, while an adapter can handle an external API. If a controller validates input, calculates business rules, formats a report, sends email, and calls a vendor API, several distinct kinds of change may be competing for one place.
Separate responsibilities where the boundary makes behavior clearer or change more local. Extracting a one-line method into a new class merely to make a class smaller can make the design harder to follow.
2. Open/Closed: extend behavior without scattering edits
The Open/Closed Principle (OCP) describes software entities as open for extension and closed for modification. In practice, it is a reason to consider a stable contract when a use case must support a meaningful variation, such as multiple payment providers or notification channels.
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Choose a seam only when variation is real
If provider-specific conditionals spread through a checkout use case, adding a new provider may require editing business logic in several places. A focused contract can let the use case call one operation while separate implementations handle provider details. The container can select the implementation at the composition boundary.
This is not a mandate to build a plugin framework for a feature that has one implementation and no credible variation. One straightforward class may be the maintainable choice until a second behavior or a testing boundary makes a seam useful.
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The Liskov Substitution Principle (LSP) says an object should be replaceable by an instance of its subtype without breaking correctness. In PHP, compatible method signatures are not enough: callers also rely on valid inputs, outputs, and error behavior.
Test the contract, not just the signature
Suppose an application has a notifier contract whose send operation promises to send a confirmation for a valid order. An implementation that silently drops messages for a class of valid orders, or throws an undocumented exception where callers expect success, may violate the useful behavioral contract even if PHP accepts the method declaration.
Document relevant expectations in the contract and test implementations against them where substitution matters. Do not mistake inheritance syntax for substitutability: the question is whether callers can rely on the same behavior.
4. Interface Segregation: avoid forcing clients to depend on unused operations
The Interface Segregation Principle (ISP) favors client-specific interfaces over one broad general-purpose interface. A reporting service that only reads invoices should not be forced to depend on write and delete operations simply because they share a large interface.
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Split by client need, not by method count
If separate consumers genuinely need different capabilities, small focused contracts can make those needs explicit and prevent a change to unrelated operations from rippling through implementations. But a tiny interface is not automatically better: several narrow abstractions can obscure a simple, stable behavior when there is only one client and one implementation.
5. Dependency Inversion: let policy depend on a useful abstraction
The Dependency Inversion Principle (DIP) says higher-level policy should depend on abstractions rather than concrete implementation details. An application service can declare the capability it needs—such as sending a notification—without knowing which mail or messaging provider performs it.
Constructor injection and container binding
Constructor injection makes a dependency visible in the class’s API and allows a test to supply a substitute. Laravel can auto-resolve many concrete classes, but when a constructor type-hints an interface, the container needs to know which implementation to use. Laravel’s documentation describes service providers as the typical place to configure bindings; use register for container bindings, not route or event registration. See the Laravel 13.x service provider documentation.
A teaching sketch follows. It illustrates one possible boundary; Laravel does not require this exact structure, and an interface is warranted only if the application benefits from the substitution or isolation.
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<?php
interface Notifier
{
public function send(Order $order): void;
}
final class ConfirmOrder
{
public function __construct(private Notifier $notifier) {}
public function handle(Order $order): void
{
// Confirm the order, then delegate the notification boundary.
$this->notifier->send($order);
}
}A concrete implementation might be EmailNotifier. Bind the contract in a service provider when Laravel must choose that implementation:
$this->app->bind(Notifier::class, EmailNotifier::class);Put that binding in the provider’s register method. If a class has no dependencies or only concrete dependencies, first check whether Laravel can resolve it without a custom binding. The container guide covers constructor injection, automatic resolution, and replacing dependencies for tests.
How to test a SOLID design in Laravel
Tests can show whether a boundary is useful: a focused unit test can exercise one small behavior with a substitute dependency, while a feature test can verify object interactions or an entire HTTP request. Laravel supports both Pest and PHPUnit and runs tests with php artisan test.
Choose the test level that matches the behavior
- Unit test: Isolate a small behavior, such as checking that
ConfirmOrderdelegates to a notifier when given an order. A substitute notifier can avoid making a real external call. - Feature test: Exercise the interaction or user-facing request flow when routing, validation, framework integration, or multiple objects are part of what must work.
Laravel’s 13.x testing guide says most tests should generally be feature tests because they provide the most confidence in overall behavior. Treat that as framework guidance, not a rule that every project or behavior needs the same test mix. A mock-heavy unit test can prove that an object called another object; it does not by itself establish that the HTTP path works.
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- Name the change. For example: “We need to send order confirmations through another channel.” Avoid designing around vague future possibilities.
- Find the current owner. Identify the class or classes that would change today, and whether they have unrelated responsibilities.
- Check for a real boundary. Is there a provider, external system, separately varying behavior, or test seam worth isolating?
- Define only the needed contract. Keep the abstraction aligned with what its client needs; do not add unrelated operations pre-emptively.
- Check substitution behavior. Specify what callers may pass, what success means, and how expected failures are reported.
- Wire the implementation at the edge. Use constructor injection; add a provider binding for an interface when Laravel cannot infer the desired concrete class.
- Test at the relevant boundary. Use a unit test for isolated behavior and a feature test for integrated or HTTP behavior.
Common design mistakes and how to correct them
- Adding an interface to every class: Prefer direct concrete injection when it is a stable, simple dependency and no substitution boundary is needed. An interface adds indirection and, in the interface-binding case, container configuration.
- Calling all dependency injection “DIP”: Injection supplies a dependency; inversion concerns which direction the design depends on. Injecting a vendor-specific concrete class can still couple application policy to a detail.
- Splitting classes just to shrink them: Separate responsibilities when they change for distinct reasons or when an extracted boundary clarifies ownership—not just to reduce line count.
- Assuming matching signatures guarantee LSP: Check expectations around inputs, outputs, side effects, and errors as well as PHP’s type compatibility.
- Building abstractions for hypothetical variation: Start with the simplest design that meets the requirement. Introduce a seam when real variation, a credible change, or isolation needs justify it.
- Expecting the container to make design decisions: Laravel resolves dependencies and applies bindings; developers still choose responsibilities and contracts.
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ScreenshotNeo is a website screenshot API and MCP server for developers, not a Laravel SOLID design pattern. If a Laravel application separately needs to capture web pages, ScreenshotNeo offers a one-request URL-to-image or PDF endpoint. The following option is separate from applying the design principles above.
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Use this cURL request to capture a page as WebP; create an API key and replace the example target URL as needed. See the ScreenshotNeo API documentation.
curl -G "https://api.screenshotneo.com/v1/shot" -d access_key=YOUR_API_KEY --data-urlencode url=https://stripe.com -o shot.webpScreenshotNeo removes cookie banners, newsletter popups, and chat widgets before capture; failed loads, bot checks, and blank pages are not billed. Its MCP server lets AI agents take screenshots, and the Free plan includes 1,000 screenshots per month with no card; paid plans start at $5 for 3,000. Sign up for ScreenshotNeo free to get 1,000 screenshots a month without a card.
Frequently Asked Questions
Does every Laravel service need an interface?
No. Use an interface when a real substitution, variation, or isolation boundary benefits the client; concrete classes can often be auto-resolved.
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Which Laravel version do the framework examples refer to?
Laravel 13.x documentation as accessed on September 29, 2026.
Is SOLID a guarantee that a Laravel application will be maintainable?
No. It is a set of design heuristics; the appropriate responsibilities and abstractions depend on the change and context.
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