Prefire: your previews are already tests. Snapshot tests, a Playbook and renders your AI agent can see, all from #Preview

Release Stars Platform Swift6 Swift Package Manager Xcode Plugins

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## 🔥 What is Prefire? Your previews are already tests. **Prefire** turns the `#Preview` blocks you write anyway into snapshot tests, a Playbook catalog and images your AI agent can see. You don't write a line of test code.

📸 Snapshot tests

Every preview becomes a snapshot test on the devices you pick. A changed padding fails the build, not the release.

How it works →

📚 Playbook

A catalog of every component and user story inside your app, with their states and render times.

See Playbook →

🤖 Renders for AI agents

Claude Code, Cursor and Codex render your previews through an MCP server and see the UI they just changed.

Set up →
> 🤖 **Using an AI agent?** `brew install barredewe/prefire/prefire`, then `claude mcp add prefire -- prefire mcp` in your project. The agent renders SwiftUI previews on any iPhone or iPad, light or dark, without Xcode Previews. [Setup →](Documentation/AI.md) ## 🚀 Key Features Playbook: user stories built from previews - 🧠 **Smart Preview Parsing** — including `#Preview`, `@Previewable` - 📸 **Snapshot Testing** — automatic test generation from previews (iOS, tvOS, macOS) - 📚 **Playbook View** — auto-generated interactive component catalog (iOS) - 🏃 **Flow-aware** — build user stories from multiple preview steps - 🤖 **AI-ready** — render previews to PNG for agents with `prefire render` and an [MCP server](Documentation/AI.md) - 🧩 **UIKit + AppKit Support** — support for `UIView`/`UIViewController` and `NSView`/`NSViewController` - ⚙️ **SPM + Xcode Plugins** — works in CLI, Xcode build phases, or CI - 🧠 **Fast Caching** — fingerprint-based AST and body caching avoids redundant work - ✍️ **Stencil Templates** — customize output with [your own templates](Documentation/Templates.md) ### Why Prefire? - 🔥 **No second set of UI states.** Tests come from the previews you already keep up to date. - 🔥 **Regressions fail CI.** Snapshots are compared on every run, on every device you list. - 🔥 **Designers and QA see every state.** Playbook shows components and user stories on a device. - 🔥 **Agents check their own UI work.** They render the previews they changed before calling a task done.
--- ## ⚡ Quick Start > 📦 Example project available at: [Prefire Example](https://github.com/BarredEwe/Prefire/tree/main/Example) ### 1. Add Prefire to Your Project ```swift // Package.swift dependencies: [ .package(url: "https://github.com/BarredEwe/Prefire.git", from: "6.3.0"), .package(url: "https://github.com/pointfreeco/swift-snapshot-testing", from: "1.18.0"), ], .testTarget( dependencies: [ .product(name: "Prefire", package: "Prefire"), .product(name: "SnapshotTesting", package: "swift-snapshot-testing"), ], plugins: [ .plugin(name: "PrefireTestsPlugin", package: "Prefire") ] ) ``` ### 2. Write `#Preview` ```swift #Preview { Button("Submit") } ``` ### 3. Run tests Just run the test target 🚀 — Prefire will auto-generate snapshots based on your previews. > 💡 If your test target is empty, Prefire will still generate files and snapshot code during build. --- ## 📦 Installation | Method | How | |--------|-----| | SPM Plugin | `PrefireTestsPlugin` / `PrefirePlaybookPlugin` in `Package.swift` | | Xcode Build Tool Plugin | Add `PrefireTestsPlugin` to the test target's build phases | | CLI | `brew install barredewe/prefire/prefire` | | Mint (*Beta*) | `mint install BarredEwe/Prefire` | | GitHub Actions / CI | Any of the above, see [Troubleshooting](#-troubleshooting) | Step-by-step setup is in the [Installation guide](Documentation/Installation.md). ### Requirements - Swift 6.0 or higher - Xcode 16.0 or higher - iOS 14 or higher; macOS 13 or higher (macOS: snapshot tests only, see [Configuration](Documentation/Configuration.md#macos-snapshot-tests)) --- ## 🛠 Usage ### Choose previews Prefire finds every **`#Preview`** automatically. For `PreviewProvider`, add the `PrefireProvider` protocol: ```swift struct Text_Previews: PreviewProvider, PrefireProvider { static var previews: some View { ... } } ``` Exclude a preview with `.prefireIgnored()`: ```swift #Preview { Text("") .prefireIgnored() } ``` To opt in instead of opting out, set `preview_default_enabled: false` in [`.prefire.yml`](#-configuration-prefireyml) and mark the previews you want with `.prefireEnabled()`: ```swift #Preview { Text("") .prefireEnabled() } ``` ### Snapshot tests `PrefireTestsPlugin` generates the tests into the DerivedData folder when the test target builds. Run the test target as usual. Tune the timing and precision of a single snapshot: ```swift #Preview { TestView() .snapshot(delay: 0.3, precision: 0.95, perceptualPrecision: 0.98) } ``` For previews that load or animate, wait instead of guessing a delay: ```swift .snapshot(waitForIdle: true) // until nothing changes on screen .snapshot(waitUntil: { viewModel.isLoaded }) // until a condition is true ``` How waiting works, its limits and how the modifiers combine: [Snapshot timing and precision](Documentation/Snapshots.md). Snapshots are compared with [swift-snapshot-testing](https://github.com/pointfreeco/swift-snapshot-testing). ### Playbook (Demo) View Show all previews as an interactive catalog with `PlaybookView`: - `isComponent: true` lists all the Views - `isComponent: false` groups them by UserStory ```swift import Prefire struct ContentView: View { var body: some View { PlaybookView(isComponent: true, previewModels: PreviewModels.models) } } ``` To keep previews and `PreviewModels` out of release builds, see [Excluding previews from release builds](Documentation/Installation.md#excluding-previews-from-release-builds). ### Flows The auth user story in Playbook: PrefireView, then AuthView Connect previews into one **Flow** with `.previewUserStory`. Playbook shows them together, in order: ```swift static var previews: some View { PrefireView() .previewUserStory(.auth) } static var previews: some View { AuthView() .previewUserStory(.auth) } ```
### States TestView in the Default and Loading states If a preview contains more than one `View`, mark the `State` of each: ```swift static var previews: some View { TestView("Default") TestView("Loading") .previewState(.loading) } ```
### Parameterized previews Prefire expands each argument of a native SwiftUI parameterized preview into its own snapshot and Playbook preview: ```swift #Preview("TextView", traits: .sizeThatFitsLayout, arguments: ["- A", "- B", "- C"]) { suffix in Text("1 \(suffix)") } ``` --- ## 🧰 API | Feature | Modifier | |--------|----------| | Include in snapshot | `.prefireEnabled()` | | Exclude from snapshot | `.prefireIgnored()` | | Group in a flow | `.previewUserStory(.auth)` | | Mark a UI state | `.previewState(.error)` | | Customize snapshot | `.snapshot(delay: 0.3, precision: 0.95)` | | Wait until the preview settles | `.snapshot(waitForIdle: true, timeout: 2.0)` | | Wait for a condition | `.snapshot(waitUntil: { viewModel.isLoaded })` | | Parameterized preview | `#Preview(..., arguments: values)` | --- ## 💡 CLI Usage ```bash # Generate snapshot tests prefire tests # Generate playbook models prefire playbook ``` Run `prefire tests --help` or `prefire playbook --help` for more options. --- ## 🤖 Let AI agents see SwiftUI Prefire renders previews in its snapshot tests, built anew and on the devices you choose, so it can show them to an AI agent as images, which Xcode Previews can't do reliably outside Xcode. An agent calls render_previews for three previews of the Trip screen and gets dark mode PNGs back ```bash # Render previews to PNG + JSON prefire render "Sign in" --device "iPhone 16 Pro" --color-scheme dark # An HTML board of the last render, grouped by user story prefire board ``` Add the MCP server to your agent, from the folder with `.prefire.yml`: | Agent | Install | | --- | --- | | Claude Code | `claude mcp add prefire -- prefire mcp`, or the plugin with a skill: `/plugin marketplace add BarredEwe/Prefire` then `/plugin install prefire@prefire` | | Cursor | [![Add to Cursor](https://cursor.com/deeplink/mcp-install-dark.svg)](https://cursor.com/en/install-mcp?name=prefire&config=eyJjb21tYW5kIjoicHJlZmlyZSIsImFyZ3MiOlsibWNwIl19) | | Codex | `codex mcp add prefire -- prefire mcp` | | VS Code | `code --add-mcp '{"name":"prefire","command":"prefire","args":["mcp"]}'` | An agent then calls `list_previews`, `render_previews` and `build_board`. Set the scheme to build in `render_configuration` of `.prefire.yml`; see the [AI guide](Documentation/AI.md). Why not Xcode's own `RenderPreview`? Prefire needs no running Xcode, renders many previews in one build, on the devices, color scheme and Dynamic Type you ask for, and works in CI. --- ## 🗂 Configuration: `.prefire.yml` ```yaml test_configuration: target: MyApp playbook_configuration: preview_default_enabled: true ``` All options are in the [Configuration guide](Documentation/Configuration.md). To change the generated code, see [Templates](Documentation/Templates.md). --- ## 🧠 How It Works 1. 🔍 **Parses all source files** — finds `#Preview` and `PreviewProvider` blocks and the `.prefireEnabled()` / `.prefireIgnored()` modifiers 2. 📂 **Caches `Types` and `PreviewBodies`** — keyed by file modification date + SHA-256 of inputs, so nothing is re-parsed if nothing changed 3. 🔢 **Generates snapshot tests** — from `Stencil` templates, respecting `.prefire.yml` 4. 📘 **Generates Playbook models** — groups by `UserStory` and `State` into `PreviewModels.generated.swift` --- ## 🩺 Troubleshooting | Problem | Fix | |---------|-----| | `NavigationView` in a preview doesn't work in Playbook | Use other views or layouts for your Playbook needs | | Plugins don't run on CI | `defaults write com.apple.dt.Xcode IDESkipPackagePluginFingerprintValidatation -bool YES` | | Xcode can't generate tests in a custom path | Disable the plugin sandbox: `defaults write com.apple.dt.Xcode IDEPackageSupportDisablePluginExecutionSandbox -bool YES` | --- ## 🐱 Also by the author Mewmori [**Mewmori**](https://mewmori.com/?src=prefire) is a pixel cat that lives on your Mac desktop. He reads what's on screen, says something about it, and remembers you between sessions. A 2B model runs on the machine through llama.cpp, so screen text, chats and memory stay on your Mac. Swift, AppKit + SwiftUI, 29 MB. Free; only skins are paid.
## 🤝 Contributing We welcome contributions! Development setup, tests and the internal architecture are described in [CONTRIBUTING.md](CONTRIBUTING.md). Logo, colors and templates for talks and posts about Prefire are in the [brand kit](https://prefire.ru/brand/). ## ⭐ Star history If Prefire saves you time, give it a star: it helps other iOS developers find it. Star history of Prefire ## 📄 License Prefire is released under the Apache License 2.0. See [LICENSE](https://github.com/BarredEwe/Prefire/blob/main/LICENSE) for details.