Capacitor Plugin Upgrade v8 to v9

Capacitor 9 is a prerelease (next dist-tag, 9.0.0-alpha.x as of October 2026). Dependency ranges below target the prerelease; after 9.0.0 GA use ^9.0.0 / from: "9.0.0". Tell the user before publishing a stable plugin release that only supports a prerelease core; a common choice is to publish it under an npm next tag.

Canonical source: https://capacitorjs.com/docs/updating/plugins/9-0

When to Use

TRIGGER when:

Plugin repo with peerDependencies["@capacitor/core"] at ^8 or >=8 and the user wants Capacitor 9 support
Plugin fails to compile against Capacitor 9 on removed APIs (CAPBridge, @NativePlugin, saveCall, getWebView(), isSimulator())
Plugin's android/build.gradle fails under AGP 9 / Gradle 9 (jcenter(), kotlin-android, proguard-android.txt, namespace collision)
A consuming app without Cordova plugins fails on the plugin's Cordova SPM product or com.getcapacitor.cordova imports

Do not use:

App projects -> capacitor-app-upgrade-v8-to-v9
Plugin still on 7 or older -> capacitor-plugin-upgrades (chain majors)
Adding SPM to a CocoaPods-only plugin -> capacitor-plugin-spm-support
Only checking a plugin against the 8.5 UIScene lifecycle -> capacitor-uiscene-migration (references/plugin-audit.md)

Live Project Snapshot

!node -e "const fs=require('fs');if(!fs.existsSync('package.json'))process.exit(0);const pkg=JSON.parse(fs.readFileSync('package.json','utf8'));const out=['package.name='+(pkg.name||''),'package.version='+(pkg.version||'')];for(const section of ['peerDependencies','dependencies','devDependencies']){for(const [name,version] of Object.entries(pkg[section]||{})){if(name.startsWith('@capacitor/'))out.push(section+'.'+name+'='+version)}}out.push('Package.swift='+fs.existsSync('Package.swift'));out.push('podspec='+fs.readdirSync('.').filter(f=>f.endsWith('.podspec')).join(','));console.log(out.join('\n'))"

!find . -maxdepth 3 \( -path './example-app' -o -path './example' -o -path './ios' -o -path './android' \) -not -path './node_modules/*'

Procedure

Inspect. Read the snapshot, android/build.gradle, android/gradle.properties, the .podspec, Package.swift, and list native sources (android/src/main, ios/Sources or ios/Plugin). Note the example app path. Confirm the tree is clean (git status).
Run the migrator from the plugin root:
shell
```
npx @capacitor/plugin-migration-v8-to-v9@latest
```
Review the diff (git diff). It covers most file edits, not API removals in your code.
Dependencies in package.json:
- devDependencies: @capacitor/cli, @capacitor/core, @capacitor/android, @capacitor/ios -> next.
- peerDependencies["@capacitor/core"]: >=9.0.0-alpha.6 (check npm view @capacitor/core dist-tags for the current prerelease). Ask whether the release should still support 8; most plugins drop it because iOS 16 / AGP 9 build changes are not backward compatible.
Build files per references/build-files.md (gradle.properties, build.gradle, podspec, Package.swift). Keep both podspec and Package.swift: apps on CocoaPods and SPM both consume the plugin.
Code API removals. Grep, then fix each hit with references/android-api-removals.md and references/ios-api-removals.md. Do not leave deprecated call paths behind #if or reflection.
Cordova optionality. Remove the unconditional .product(name: "Cordova", ...) from Package.swift. If the plugin's native code imports Cordova compatibility classes (com.getcapacitor.cordova.*, CDV*) it will break in apps without Cordova plugins; ask the user how to replace it.
UIScene lifecycle. Every Capacitor 9 app is scene-based. Audit iOS code for AppDelegate-method assumptions, tmpWindow, keyWindow presentation, applicationState (see capacitor-uiscene-migration -> references/plugin-audit.md). Since the minimum is now 9, .capacitorScene* notifications and SceneDelegateProxy are safe to use.
Example app and docs. Upgrade the example app with capacitor-app-upgrade-v8-to-v9. Update README install/compat tables (Capacitor 9, iOS 16, minSdk 26).
Verify with references/verification.md. Bump the plugin major version.

Traps

AGP 9 defaults android.uniquePackageNames=true: a scaffold default namespace (com.mycompany.plugins.example) or a fork that kept the upstream namespace now fails the consuming app's build. Make it unique.
targetSdkVersion in a library module has no runtime effect; delete it rather than bumping.
CapacitorUrlRequest.setRequestHeaders([String: Any]) sets values instead of appending; repeated header keys now overwrite.
Package.swift must point at capacitor-swift-pm from: "9.0.0-alpha.6" or later (earlier alphas had Cordova-optionality crashes). Use the newest alpha.
googleMapsUtilsVersion 5.0.0 carries upstream breaking API changes.
Running npx cap sync from the plugin root does nothing useful; sync inside the example app.

Error Handling

Error	Fix
cannot find symbol ... class NativePlugin	@CapacitorPlugin(name = ..., permissions = ...)
cannot find symbol ... method saveCall(PluginCall)	call.setKeepAlive(true) or bridge.saveCall(call)
cannot find symbol ... method pluginRequestPermission(...)	requestPermissionForAlias(alias, call, "callbackName") + @PermissionCallback
Cannot find 'CAPBridge' in scope	ApplicationDelegateProxy.shared / Notification.Name.capacitorStatusBarTapped
Value of type 'CAPBridgeProtocol' has no member 'getWebView'	bridge?.webView (same pattern for other getters -> properties)
Duplicate or conflicting Kotlin plugin error under AGP 9	Remove standalone Kotlin plugin and stdlib
Namespace collision / duplicate package in consuming app	Unique namespace in android/build.gradle
SPM resolution or link error mentioning Cordova in a consuming app	Remove the Cordova product dependency

References

Only load a reference when its topic is in play.

File	Load when
references/build-files.md	Editing gradle.properties, build.gradle, podspec, Package.swift, wrapper
references/android-api-removals.md	Any Java/Kotlin compile error or grep hit
references/ios-api-removals.md	Any Swift/ObjC compile error or grep hit
references/verification.md	After edits: greps, builds, example-app checks, publish

Related skills: capacitor-plugin-upgrades, capacitor-app-upgrade-v8-to-v9, capacitor-uiscene-migration, capacitor-plugin-spm-support.

@capgo/capgo-skills