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Angular’s DI error code and dependency path usually point to the right fix. NG0201 means no provider was found for a token; NG0203 means inject() ran outside an injection context; and NG0200 identifies a circular dependency. Start with the exact error, trace the named token or dependency chain, then check provider reachability, injection timing, or a cycle as appropriate.
Angular’s documentation says DI issues typically stem from “configuration mistakes, scope problems, or incorrect usage patterns.” The guide below follows those failure classes rather than treating every DI error as a registration problem. Angular: Debugging and troubleshooting DI.
Start with the error code and dependency path
Copy the full error, including its code, token name, and any dependency path or stack trace. Do not assume the first service named is the root cause: a consumer may be registered correctly but depend on another token that is missing, unavailable in its injector scope, or part of a cycle.
- Identify the failure class. NG0201 points to a missing provider; NG0203 points to invalid
inject()timing or context; NG0200 points to a dependency cycle. - Trace the chain. Follow each dependency in the reported path until you reach the token Angular cannot resolve, the call where
inject()runs, or the point where the chain returns to an earlier service. - Check where and when. For NG0201, inspect the consumer’s injector ancestry. For NG0203, locate the actual execution of
inject(). For NG0200, map direct and indirect dependencies. - Verify with tools or a smaller case. Inspect provider locations with Angular DevTools, add targeted logging if needed, and reduce a complicated case to a minimal component or test.
Official error references: NG0201, NG0203, and NG0200.
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How to fix NG0201: No provider for a token
NG0201 means Angular tried to resolve a dependency but could not find a provider for the requested token in an injector available to the requesting code. Read the reported token and dependency path, then work backward: determine which class requests it, which provider supplies it, and whether that provider is registered in an injector the consumer can reach.
Check provider registration and token identity
- Confirm the intended service is decorated and configured for your application’s Angular version. Depending on the app’s setup, a service may use a service decorator or be registered in an NgModule’s
providers; follow the applicable provider configuration rather than copying a setup from a different Angular version. - Check that the consumer requests the same runtime token that was provided. A TypeScript interface cannot serve as a DI token because interfaces are erased at runtime. Use an
InjectionTokenfor an interface-backed value and provide a value for that token. - Check the entire dependency chain. The named service may be available while one of its own constructor dependencies is not.
See Angular’s guides to troubleshooting DI and defining dependency providers.
Distinguish an absent provider from the wrong scope
A provider declared in a component’s providers belongs to that component’s injector and is available to the component and its descendants. It is not available to the component’s parent or siblings. If a consumer outside that subtree requests the token, registering it only on the component will not satisfy that request.
Open Angular DevTools and inspect the injector tree to see where the provider exists. If the service is intentionally component-scoped, move the consumer into that scope or provide the token at a scope reachable by both. If multiple components declare the same provider, they may each receive a separate instance; inspect the tree and compare the instances when unexpected state separation suggests duplication.
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How to fix NG0203: inject() outside an injection context
NG0203 means inject() ran when Angular was not establishing or running an injection context. The location where the expression is written is not enough to judge: find when it executes. A field initializer runs during object construction, but a method called later does not automatically have an injection context.
Capture dependencies while Angular creates the class
Use inject() during DI-managed construction, such as in a class field initializer, or use constructor injection. Do not call it from a lifecycle hook or an ordinary later method:
import { inject } from '@angular/core';
import { ApiService } from './api.service';
class ExampleComponent {
private readonly api = inject(ApiService);
loadData() {
return this.api.load();
}
}Here, the dependency is captured during construction; the later method uses the stored reference rather than asking Angular to resolve it again.
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Handle deferred work deliberately
An asynchronous callback or other deferred function does not inherit an injection context just because it was created by a class that had one. Capture the needed dependency before scheduling the callback. If code genuinely must resolve a dependency later, use runInInjectionContext with an injector, following the API requirements for your Angular version.
Angular documents the valid contexts and the runInInjectionContext approach in its NG0203 reference and DI troubleshooting guide.
How to fix NG0200: Circular dependency
NG0200 means resolving a dependency leads back to a dependency already being resolved. The loop can be indirect: for example, one service needs a second service, which needs a third, which then needs the first. Follow the error path or call stack until the chain returns to its starting token.
- Write down each service or token in the reported chain in order.
- Mark the dependency that closes the loop, including dependencies introduced through factories or other providers.
- Refactor to remove the interdependence—often by moving shared responsibilities into a separate service or changing which class owns an operation.
Angular’s guidance is to remove or refactor the dependency loop. Do not treat forwardRef, which addresses certain forward-reference situations, as a general fix for a service dependency cycle. See Angular’s NG0200 reference.
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When the error remains unclear
- Inspect the injector tree: Angular DevTools can show which providers are present at each level and help distinguish a missing registration from a scope mismatch.
- Add focused logging: Use it to confirm which consumer or provider path is being reached when the injector view is insufficient.
- Reduce the dependency graph: Remove dependencies one at a time and reproduce the issue in a minimal component or test. This can expose the specific missing token, invalid call timing, or cycle without unrelated application code.
- Check version-specific guidance: Angular documentation evolves; confirm provider configuration and API examples against the Angular version installed in the project. The documentation pages reviewed for this guide reported Angular v22.2.1+sha-fa63bfa in their footer on October 7, 2026.
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