## Building APIs

| Pattern | Skill Level | Summary |
| :--- | :--- | :--- |
| [Handle a GET Request](./content/published/handle-get-request.mdx) | 🟢 **Beginner** | Define a route that responds to a specific HTTP GET request path. |
| [Send a JSON Response](./content/published/send-json-response.mdx) | 🟢 **Beginner** | Create and send a structured JSON response with the correct headers and status code. |
| [Extract Path Parameters](./content/published/extract-path-parameters.mdx) | 🟢 **Beginner** | Capture and use dynamic segments from a request URL, such as a resource ID. |
| [Create a Basic HTTP Server](./content/published/launch-http-server.mdx) | 🟢 **Beginner** | Launch a simple, effect-native HTTP server to respond to incoming requests. |
| [Validate Request Body](./content/published/validate-request-body.mdx) | 🟡 **Intermediate** | Safely parse and validate an incoming JSON request body against a predefined Schema. |
| [Provide Dependencies to Routes](./content/published/provide-dependencies-to-routes.mdx) | 🟡 **Intermediate** | Inject services like database connections into HTTP route handlers using Layer and Effect.Service. |
| [Handle API Errors](./content/published/handle-api-errors.mdx) | 🟡 **Intermediate** | Translate application-specific errors from the Effect failure channel into meaningful HTTP error responses. |
| [Make an Outgoing HTTP Client Request](./content/published/make-http-client-request.mdx) | 🟡 **Intermediate** | Use the built-in Effect HTTP client to make safe and composable requests to external services from within your API. |

## Core Concepts

## Concurrency

## Testing

| Pattern | Skill Level | Summary |
| :--- | :--- | :--- |
| [Accessing the Current Time with Clock](./content/published/accessing-current-time-with-clock.mdx) | 🟡 **Intermediate** | Use the Clock service to access the current time in a testable, deterministic way, avoiding direct calls to Date.now(). |
| [Write Tests That Adapt to Application Code](./content/published/write-tests-that-adapt-to-application-code.mdx) | 🟡 **Intermediate** | A cardinal rule of testing: Tests must adapt to the application's interface, not the other way around. Never modify application code solely to make a test pass. |
| [Use the Auto-Generated .Default Layer in Tests](./content/published/use-default-layer-for-tests.mdx) | 🟡 **Intermediate** | When testing, always use the MyService.Default layer that is automatically generated by the Effect.Service class for dependency injection. |
| [Mocking Dependencies in Tests](./content/published/mocking-dependencies-in-tests.mdx) | 🟡 **Intermediate** | Use a test-specific Layer to provide mock implementations of services your code depends on, enabling isolated and deterministic unit tests. |
| [Model Dependencies as Services](./content/published/model-dependencies-as-services.mdx) | 🟡 **Intermediate** | Abstract external dependencies and capabilities into swappable, testable services using Effect's dependency injection system. |
| [Create a Testable HTTP Client Service](./content/published/create-a-testable-http-client-service.mdx) | 🟡 **Intermediate** | Define an HttpClient service with separate 'Live' and 'Test' layers to enable robust, testable interactions with external APIs. |
| [Organize Layers into Composable Modules](./content/published/organize-layers-into-composable-modules.mdx) | 🟠 **Advanced** | Structure a large application by grouping related services into 'module' layers, which are then composed together with a shared base layer. |

## Tooling and Debugging

| Pattern | Skill Level | Summary |
| :--- | :--- | :--- |
| [Supercharge Your Editor with the Effect LSP](./content/published/supercharge-your-editor-with-the-effect-lsp.mdx) | 🟡 **Intermediate** | Install the Effect Language Server (LSP) extension for your editor to get rich, inline type information and enhanced error checking for your Effect code. |
| [Teach your AI Agents Effect with the MCP Server](./content/published/teach-your-ai-agents-effect-with-the-mcp-server.mdx) | 🟠 **Advanced** | Use the Effect MCP server to provide live, contextual information about your application's structure directly to AI coding agents. |

## Domain Modeling

## Modeling Data

| Pattern | Skill Level | Summary |
| :--- | :--- | :--- |
| [Comparing Data by Value with Structural Equality](./content/published/comparing-data-by-value-with-structural-equality.mdx) | 🟢 **Beginner** | Use Data.struct and Equal.equals to safely compare objects by their value instead of their reference, avoiding common JavaScript pitfalls. |

## Making HTTP Requests

| Pattern | Skill Level | Summary |
| :--- | :--- | :--- |
| [Add Custom Metrics to Your Application](./content/published/add-custom-metrics.mdx) | 🟡 **Intermediate** | Use Effect's Metric module to instrument your code with counters, gauges, and histograms to track key business and performance indicators. |
| [Model Dependencies as Services](./content/published/model-dependencies-as-services.mdx) | 🟡 **Intermediate** | Abstract external dependencies and capabilities into swappable, testable services using Effect's dependency injection system. |
| [Create a Testable HTTP Client Service](./content/published/create-a-testable-http-client-service.mdx) | 🟡 **Intermediate** | Define an HttpClient service with separate 'Live' and 'Test' layers to enable robust, testable interactions with external APIs. |
| [Add Caching by Wrapping a Layer](./content/published/add-caching-by-wrapping-a-layer.mdx) | 🟠 **Advanced** | Implement caching by creating a new layer that wraps a live service, intercepting method calls to add caching logic without modifying the original service. |
| [Build a Basic HTTP Server](./content/published/build-a-basic-http-server.mdx) | 🟠 **Advanced** | Combine Layer, Runtime, and Effect to create a simple, robust HTTP server using Node.js's built-in http module. |
| [Create a Managed Runtime for Scoped Resources](./content/published/create-managed-runtime-for-scoped-resources.mdx) | 🟠 **Advanced** | Use Layer.launch to safely manage the lifecycle of layers containing scoped resources, ensuring finalizers are always run. |

## Observability

| Pattern | Skill Level | Summary |
| :--- | :--- | :--- |
| [Add Custom Metrics to Your Application](./content/published/add-custom-metrics.mdx) | 🟡 **Intermediate** | Use Effect's Metric module to instrument your code with counters, gauges, and histograms to track key business and performance indicators. |
| [Trace Operations Across Services with Spans](./content/published/trace-operations-with-spans.mdx) | 🟡 **Intermediate** | Use Effect.withSpan to create custom tracing spans, providing detailed visibility into the performance and flow of your application's operations. |

## Resource Management

| Pattern | Skill Level | Summary |
| :--- | :--- | :--- |
| [Safely Bracket Resource Usage with `acquireRelease`](./content/published/safely-bracket-resource-usage.mdx) | 🟢 **Beginner** | Use `Effect.acquireRelease` to guarantee a resource's cleanup logic runs, even if errors or interruptions occur. |
| [Create a Service Layer from a Managed Resource](./content/published/scoped-service-layer.mdx) | 🟡 **Intermediate** | Use `Layer.scoped` with `Effect.Service` to transform a managed resource into a shareable, application-wide service. |
| [Compose Resource Lifecycles with `Layer.merge`](./content/published/compose-scoped-layers.mdx) | 🟡 **Intermediate** | Combine multiple resource-managing layers, letting Effect automatically handle the acquisition and release order. |
| [Manage Resource Lifecycles with Scope](./content/published/manage-resource-lifecycles-with-scope.mdx) | 🟠 **Advanced** | Use Scope for fine-grained, manual control over resource lifecycles, ensuring cleanup logic (finalizers) is always executed. |
| [Manually Manage Lifecycles with `Scope`](./content/published/manual-scope-management.mdx) | 🟠 **Advanced** | Use `Scope` directly to manage complex resource lifecycles or when building custom layers. |
| [Implement Graceful Shutdown for Your Application](./content/published/implement-graceful-shutdown.mdx) | 🟠 **Advanced** | Use Effect.runFork and listen for OS signals (SIGINT, SIGTERM) to trigger a Fiber.interrupt, ensuring all resources are safely released. |
| [Create a Managed Runtime for Scoped Resources](./content/published/create-managed-runtime-for-scoped-resources.mdx) | 🟠 **Advanced** | Use Layer.launch to safely manage the lifecycle of layers containing scoped resources, ensuring finalizers are always run. |

## File Handling

| Pattern | Skill Level | Summary |
| :--- | :--- | :--- |
| [Safely Bracket Resource Usage with `acquireRelease`](./content/published/safely-bracket-resource-usage.mdx) | 🟢 **Beginner** | Use `Effect.acquireRelease` to guarantee a resource's cleanup logic runs, even if errors or interruptions occur. |

## Database Connections

| Pattern | Skill Level | Summary |
| :--- | :--- | :--- |
| [Safely Bracket Resource Usage with `acquireRelease`](./content/published/safely-bracket-resource-usage.mdx) | 🟢 **Beginner** | Use `Effect.acquireRelease` to guarantee a resource's cleanup logic runs, even if errors or interruptions occur. |

## Network Requests

| Pattern | Skill Level | Summary |
| :--- | :--- | :--- |
| [Safely Bracket Resource Usage with `acquireRelease`](./content/published/safely-bracket-resource-usage.mdx) | 🟢 **Beginner** | Use `Effect.acquireRelease` to guarantee a resource's cleanup logic runs, even if errors or interruptions occur. |

## Building Data Pipelines

| Pattern | Skill Level | Summary |
| :--- | :--- | :--- |
| [Create a Stream from a List](./content/published/stream-from-iterable.mdx) | 🟢 **Beginner** | Turn a simple in-memory array or list into a foundational data pipeline using Stream. |
| [Run a Pipeline for its Side Effects](./content/published/stream-run-for-effects.mdx) | 🟢 **Beginner** | Execute a pipeline for its effects without collecting the results, saving memory. |
| [Collect All Results into a List](./content/published/stream-collect-results.mdx) | 🟢 **Beginner** | Run a pipeline and gather all of its results into an in-memory array. |
| [Turn a Paginated API into a Single Stream](./content/published/stream-from-paginated-api.mdx) | 🟡 **Intermediate** | Convert a paginated API into a continuous, easy-to-use stream, abstracting away the complexity of fetching page by page. |
| [Process Items Concurrently](./content/published/stream-process-concurrently.mdx) | 🟡 **Intermediate** | Perform an asynchronous action for each item in a stream with controlled parallelism to dramatically improve performance. |
| [Process Items in Batches](./content/published/stream-process-in-batches.mdx) | 🟡 **Intermediate** | Group items into chunks for efficient bulk operations, like database inserts or batch API calls. |
| [Process collections of data asynchronously](./content/published/process-a-collection-of-data-asynchronously.mdx) | 🟡 **Intermediate** | Process collections of data asynchronously in a lazy, composable, and resource-safe manner using Effect's Stream. |
| [Process a Large File with Constant Memory](./content/published/stream-from-file.mdx) | 🟡 **Intermediate** | Create a data pipeline from a file on disk, processing it line-by-line without loading the entire file into memory. |
| [Automatically Retry Failed Operations](./content/published/stream-retry-on-failure.mdx) | 🟡 **Intermediate** | Build a self-healing pipeline that can automatically retry failed processing steps using a configurable backoff strategy. |
| [Manage Resources Safely in a Pipeline](./content/published/stream-manage-resources.mdx) | 🟠 **Advanced** | Ensure resources like file handles or connections are safely acquired at the start of a pipeline and always released at the end, even on failure. |

## Application Configuration

| Pattern | Skill Level | Summary |
| :--- | :--- | :--- |
| [Access Configuration from the Context](./content/published/access-config-in-context.mdx) | 🟡 **Intermediate** | Access your type-safe configuration within an Effect.gen block by yielding the Config object you defined. |
| [Define a Type-Safe Configuration Schema](./content/published/define-config-schema.mdx) | 🟡 **Intermediate** | Use Effect.Config primitives to define a schema for your application's configuration, ensuring type-safety and separation from code. |
| [Provide Configuration to Your App via a Layer](./content/published/provide-config-layer.mdx) | 🟡 **Intermediate** | Use Config.layer(schema) to create a Layer that provides your configuration schema to the application's context. |

## Modeling Time

| Pattern | Skill Level | Summary |
| :--- | :--- | :--- |
| [Accessing the Current Time with Clock](./content/published/accessing-current-time-with-clock.mdx) | 🟡 **Intermediate** | Use the Clock service to access the current time in a testable, deterministic way, avoiding direct calls to Date.now(). |
| [Representing Time Spans with Duration](./content/published/representing-time-spans-with-duration.mdx) | 🟡 **Intermediate** | Use the Duration data type to represent time intervals in a type-safe, human-readable, and composable way. |
| [Beyond the Date Type - Real World Dates, Times, and Timezones](./content/published/beyond-the-date-type.mdx) | 🟡 **Intermediate** | Use the Clock service for testable access to the current time and prefer immutable primitives for storing and passing timestamps. |

## Project Setup & Execution

| Pattern | Skill Level | Summary |
| :--- | :--- | :--- |
| [Execute Synchronous Effects with Effect.runSync](./content/published/execute-with-runsync.mdx) | 🟢 **Beginner** | Use Effect.runSync at the 'end of the world' to execute a purely synchronous Effect and get its value directly. |
| [Execute Asynchronous Effects with Effect.runPromise](./content/published/execute-with-runpromise.mdx) | 🟢 **Beginner** | Use Effect.runPromise at the 'end of the world' to execute an asynchronous Effect and get its result as a JavaScript Promise. |
| [Set Up a New Effect Project](./content/published/setup-new-project.mdx) | 🟢 **Beginner** | Initialize a new Node.js project with the necessary TypeScript configuration and Effect dependencies to start building. |
| [Execute Long-Running Apps with Effect.runFork](./content/published/execute-long-running-apps-with-runfork.mdx) | 🟠 **Advanced** | Use Effect.runFork at the application's entry point to launch a long-running process as a detached fiber, allowing for graceful shutdown. |
| [Create a Reusable Runtime from Layers](./content/published/create-reusable-runtime-from-layers.mdx) | 🟠 **Advanced** | Compile your application's layers into a reusable Runtime object to efficiently execute multiple effects that share the same context. |
| [Create a Managed Runtime for Scoped Resources](./content/published/create-managed-runtime-for-scoped-resources.mdx) | 🟠 **Advanced** | Use Layer.launch to safely manage the lifecycle of layers containing scoped resources, ensuring finalizers are always run. |

## Advanced Dependency Injection

| Pattern | Skill Level | Summary |
| :--- | :--- | :--- |
| [Manually Manage Lifecycles with `Scope`](./content/published/manual-scope-management.mdx) | 🟠 **Advanced** | Use `Scope` directly to manage complex resource lifecycles or when building custom layers. |

## Custom Layers

| Pattern | Skill Level | Summary |
| :--- | :--- | :--- |
| [Manually Manage Lifecycles with `Scope`](./content/published/manual-scope-management.mdx) | 🟠 **Advanced** | Use `Scope` directly to manage complex resource lifecycles or when building custom layers. |

## Dependency Injection

| Pattern | Skill Level | Summary |
| :--- | :--- | :--- |
| [Create a Service Layer from a Managed Resource](./content/published/scoped-service-layer.mdx) | 🟡 **Intermediate** | Use `Layer.scoped` with `Effect.Service` to transform a managed resource into a shareable, application-wide service. |
| [Compose Resource Lifecycles with `Layer.merge`](./content/published/compose-scoped-layers.mdx) | 🟡 **Intermediate** | Combine multiple resource-managing layers, letting Effect automatically handle the acquisition and release order. |

## Application Architecture