diff --git a/src/first-party/auto-inject.ts b/src/first-party/auto-inject.ts
index 1d27a80cf..0a57cdcd0 100644
--- a/src/first-party/auto-inject.ts
+++ b/src/first-party/auto-inject.ts
@@ -51,22 +51,36 @@ export function autoInjectProxyEndpoints(
 ): void {
   for (const def of AUTO_INJECT_DEFS) {
     const entry = registry[def.registryKey]
-    if (!entry || typeof entry !== 'object')
+    if (!entry)
       continue
 
-    const config = (Array.isArray(entry) ? entry[0] : entry) as Record<string, any>
+    const rtScripts = runtimeConfig.public?.scripts as Record<string, any> | undefined
+    const rtEntry = rtScripts?.[def.registryKey]
+    const rtConfig = rtEntry && typeof rtEntry === 'object'
+      ? (Array.isArray(rtEntry) ? rtEntry[0] : rtEntry)
+      : undefined
+
+    let config: Record<string, any> | undefined
+    if (entry === true || entry === 'mock') {
+      config = rtConfig || {}
+    }
+    else if (typeof entry === 'object') {
+      config = (Array.isArray(entry) ? entry[0] : entry) as Record<string, any>
+    }
+
     if (!config || config[def.configField])
       continue
 
-    config[def.configField] = def.computeValue(collectPrefix, config)
+    const value = def.computeValue(collectPrefix, config)
+
+    if (typeof entry === 'object') {
+      config[def.configField] = value
+    }
 
     // Propagate to runtimeConfig
-    const rtScripts = runtimeConfig.public?.scripts as Record<string, any> | undefined
-    const rtEntry = rtScripts?.[def.registryKey]
     if (rtEntry && typeof rtEntry === 'object') {
-      const rtConfig = Array.isArray(rtEntry) ? rtEntry[0] : rtEntry
       if (rtConfig)
-        rtConfig[def.configField] = config[def.configField]
+        rtConfig[def.configField] = value
     }
   }
 }
diff --git a/test/unit/auto-inject.test.ts b/test/unit/auto-inject.test.ts
new file mode 100644
index 000000000..1730b3169
--- /dev/null
+++ b/test/unit/auto-inject.test.ts
@@ -0,0 +1,178 @@
+import { describe, expect, it } from 'vitest'
+import { autoInjectProxyEndpoints } from '../../src/first-party/auto-inject'
+
+function makeRuntimeConfig(scripts: Record<string, any> = {}) {
+  return { public: { scripts } }
+}
+
+describe('autoInjectProxyEndpoints', () => {
+  describe('object entries', () => {
+    it('injects apiHost for posthog config object', () => {
+      const registry: any = { posthog: { apiKey: 'phc_test' } }
+      const rt = makeRuntimeConfig({ posthog: { apiKey: 'phc_test' } })
+
+      autoInjectProxyEndpoints(registry, rt, '/_proxy')
+
+      expect(registry.posthog.apiHost).toBe('/_proxy/ph')
+      expect(rt.public.scripts.posthog.apiHost).toBe('/_proxy/ph')
+    })
+
+    it('injects endpoint for plausible config object', () => {
+      const registry: any = { plausibleAnalytics: { domain: 'example.com' } }
+      const rt = makeRuntimeConfig({ plausibleAnalytics: { domain: 'example.com' } })
+
+      autoInjectProxyEndpoints(registry, rt, '/_proxy')
+
+      expect(registry.plausibleAnalytics.endpoint).toBe('/_proxy/plausible/api/event')
+      expect(rt.public.scripts.plausibleAnalytics.endpoint).toBe('/_proxy/plausible/api/event')
+    })
+
+    it('does not override existing config field', () => {
+      const registry: any = { posthog: { apiKey: 'phc_test', apiHost: 'https://custom.host' } }
+      const rt = makeRuntimeConfig({ posthog: { apiKey: 'phc_test', apiHost: 'https://custom.host' } })
+
+      autoInjectProxyEndpoints(registry, rt, '/_proxy')
+
+      expect(registry.posthog.apiHost).toBe('https://custom.host')
+      expect(rt.public.scripts.posthog.apiHost).toBe('https://custom.host')
+    })
+
+    it('uses EU prefix when posthog region is eu', () => {
+      const registry: any = { posthog: { apiKey: 'phc_test', region: 'eu' } }
+      const rt = makeRuntimeConfig({ posthog: { apiKey: 'phc_test', region: 'eu' } })
+
+      autoInjectProxyEndpoints(registry, rt, '/_proxy')
+
+      expect(registry.posthog.apiHost).toBe('/_proxy/ph-eu')
+    })
+  })
+
+  describe('array entries', () => {
+    it('injects into first element of array entry', () => {
+      const registry: any = { posthog: [{ apiKey: 'phc_test' }, { partytown: true }] }
+      const rt = makeRuntimeConfig({ posthog: { apiKey: 'phc_test' } })
+
+      autoInjectProxyEndpoints(registry, rt, '/_proxy')
+
+      expect(registry.posthog[0].apiHost).toBe('/_proxy/ph')
+      expect(rt.public.scripts.posthog.apiHost).toBe('/_proxy/ph')
+    })
+
+    it('skips empty array entries', () => {
+      const registry: any = { posthog: [] }
+      const rt = makeRuntimeConfig({ posthog: { apiKey: '' } })
+
+      autoInjectProxyEndpoints(registry, rt, '/_proxy')
+
+      expect(rt.public.scripts.posthog.apiHost).toBeUndefined()
+    })
+  })
+
+  describe('boolean entries', () => {
+    it('injects into runtimeConfig for posthog: true', () => {
+      const registry: any = { posthog: true }
+      const rt = makeRuntimeConfig({ posthog: { apiKey: '' } })
+
+      autoInjectProxyEndpoints(registry, rt, '/_proxy')
+
+      expect(registry.posthog).toBe(true)
+      expect(rt.public.scripts.posthog.apiHost).toBe('/_proxy/ph')
+    })
+
+    it('uses EU prefix for posthog: true when runtime region is eu', () => {
+      const registry: any = { posthog: true }
+      const rt = makeRuntimeConfig({ posthog: { apiKey: '', region: 'eu' } })
+
+      autoInjectProxyEndpoints(registry, rt, '/_proxy')
+
+      expect(rt.public.scripts.posthog.apiHost).toBe('/_proxy/ph-eu')
+    })
+
+    it('injects into runtimeConfig for plausibleAnalytics: true', () => {
+      const registry: any = { plausibleAnalytics: true }
+      const rt = makeRuntimeConfig({ plausibleAnalytics: { domain: '' } })
+
+      autoInjectProxyEndpoints(registry, rt, '/_proxy')
+
+      expect(rt.public.scripts.plausibleAnalytics.endpoint).toBe('/_proxy/plausible/api/event')
+    })
+
+    it('injects into runtimeConfig for umamiAnalytics: true', () => {
+      const registry: any = { umamiAnalytics: true }
+      const rt = makeRuntimeConfig({ umamiAnalytics: { websiteId: '' } })
+
+      autoInjectProxyEndpoints(registry, rt, '/_proxy')
+
+      expect(rt.public.scripts.umamiAnalytics.hostUrl).toBe('/_proxy/umami')
+    })
+
+    it('injects into runtimeConfig for rybbitAnalytics: true', () => {
+      const registry: any = { rybbitAnalytics: true }
+      const rt = makeRuntimeConfig({ rybbitAnalytics: { siteId: '' } })
+
+      autoInjectProxyEndpoints(registry, rt, '/_proxy')
+
+      expect(rt.public.scripts.rybbitAnalytics.analyticsHost).toBe('/_proxy/rybbit/api')
+    })
+
+    it('injects into runtimeConfig for databuddyAnalytics: true', () => {
+      const registry: any = { databuddyAnalytics: true }
+      const rt = makeRuntimeConfig({ databuddyAnalytics: { clientId: '' } })
+
+      autoInjectProxyEndpoints(registry, rt, '/_proxy')
+
+      expect(rt.public.scripts.databuddyAnalytics.apiUrl).toBe('/_proxy/databuddy-api')
+    })
+  })
+
+  describe('mock entries', () => {
+    it('injects into runtimeConfig for posthog: mock', () => {
+      const registry: any = { posthog: 'mock' }
+      const rt = makeRuntimeConfig({ posthog: { apiKey: '' } })
+
+      autoInjectProxyEndpoints(registry, rt, '/_proxy')
+
+      expect(rt.public.scripts.posthog.apiHost).toBe('/_proxy/ph')
+    })
+  })
+
+  describe('skipped entries', () => {
+    it('skips scripts not in AUTO_INJECT_DEFS', () => {
+      const registry: any = { googleAnalytics: { id: 'G-TEST' } }
+      const rt = makeRuntimeConfig({ googleAnalytics: { id: 'G-TEST' } })
+
+      autoInjectProxyEndpoints(registry, rt, '/_proxy')
+
+      expect(rt.public.scripts.googleAnalytics).toEqual({ id: 'G-TEST' })
+    })
+
+    it('skips falsy entries', () => {
+      const registry: any = { posthog: false }
+      const rt = makeRuntimeConfig()
+
+      autoInjectProxyEndpoints(registry, rt, '/_proxy')
+
+      expect(rt.public.scripts.posthog).toBeUndefined()
+    })
+
+    it('does not modify existing runtimeConfig for falsy entry', () => {
+      const registry: any = { posthog: false }
+      const rt = makeRuntimeConfig({ posthog: { existing: 'value' } })
+
+      autoInjectProxyEndpoints(registry, rt, '/_proxy')
+
+      expect(rt.public.scripts.posthog).toEqual({ existing: 'value' })
+    })
+  })
+
+  describe('custom collectPrefix', () => {
+    it('uses custom prefix in computed values', () => {
+      const registry: any = { posthog: true }
+      const rt = makeRuntimeConfig({ posthog: { apiKey: '' } })
+
+      autoInjectProxyEndpoints(registry, rt, '/_analytics')
+
+      expect(rt.public.scripts.posthog.apiHost).toBe('/_analytics/ph')
+    })
+  })
+})