diff --git a/packages/dev/README.md b/packages/dev/README.md
index 05448d2c9..f9c70940f 100644
--- a/packages/dev/README.md
+++ b/packages/dev/README.md
@@ -30,7 +30,12 @@ import { NetlifyDev } from '@netlify/dev'
 const devServer = new NetlifyDev({
   blobs: { enabled: true },
   edgeFunctions: { enabled: true },
-  environmentVariables: { enabled: true },
+  environmentVariables: {
+    enabled: true,
+    // OPTIONAL: control whether user-defined environment variables are injected
+    // When false, only platform env vars (NETLIFY_LOCAL, CONTEXT, SITE_ID, etc.) are injected
+    injectUserEnv: true, // default: true
+  },
   functions: { enabled: true },
   redirects: { enabled: true },
   staticFiles: {
diff --git a/packages/dev/src/lib/env.ts b/packages/dev/src/lib/env.ts
index 344af494b..5198f2433 100644
--- a/packages/dev/src/lib/env.ts
+++ b/packages/dev/src/lib/env.ts
@@ -42,10 +42,26 @@ interface InjectEnvironmentVariablesOptions {
   accountSlug?: string
   baseVariables: Record<string, EnvironmentVariable>
   envAPI: EnvironmentVariables
+  /**
+   * Whether to inject user-defined environment variables.
+   * When false, only platform environment variables (from 'general' and 'internal' sources)
+   * are injected. When true, all environment variables are injected.
+   * @default true
+   */
+  injectUserEnv?: boolean
   netlifyAPI?: NetlifyAPI
   siteID?: string
 }
 
+/**
+ * Determines if an environment variable is a platform variable.
+ * Platform variables are from 'general' or 'internal' sources and include
+ * documented runtime variables like NETLIFY_LOCAL, CONTEXT, SITE_ID, etc.
+ */
+const isPlatformEnvironmentVariable = (variable: EnvironmentVariable): boolean => {
+  return variable.sources.includes('general') || variable.sources.includes('internal')
+}
+
 /**
  * Inject user-defined environment variables (from various sources, see `@netlify/config`)
  * into the provided `envAPI` (which may be a proxy to `process.env`, affecting the current proc),
@@ -61,6 +77,7 @@ export const injectEnvVariables = async ({
   accountSlug,
   baseVariables = {},
   envAPI,
+  injectUserEnv = true,
   netlifyAPI,
   siteID,
 }: InjectEnvironmentVariablesOptions) => {
@@ -80,6 +97,11 @@ export const injectEnvVariables = async ({
   // Inject env vars which come from multiple `source`s and have been collected from
   // `@netlify/config` and/or Envelope. These have not been populated on the actual env yet.
   for (const [key, variable] of Object.entries(variables)) {
+    // If injectUserEnv is false, only inject platform env vars (from 'general' and 'internal' sources)
+    if (!injectUserEnv && !isPlatformEnvironmentVariable(variable)) {
+      continue
+    }
+
     const existsInProcess = envAPI.has(key)
     const [usedSource, ...overriddenSources] = existsInProcess ? ['process', ...variable.sources] : variable.sources
     const isInternal = variable.sources.includes('internal')
diff --git a/packages/dev/src/main.test.ts b/packages/dev/src/main.test.ts
index 968a1dfaf..d9af7a027 100644
--- a/packages/dev/src/main.test.ts
+++ b/packages/dev/src/main.test.ts
@@ -1107,3 +1107,84 @@ describe('Handling requests', () => {
     })
   })
 })
+
+describe('Environment variable injection', () => {
+  afterEach(() => {
+    vi.unstubAllEnvs()
+  })
+
+  test('injectUserEnv option controls user-defined env var injection', async () => {
+    const fixture = new Fixture()
+      .withFile(
+        'netlify.toml',
+        `[build]
+         publish = "public"
+         [context.dev.environment]
+         MY_USER_VAR = "user value"
+      `,
+      )
+      .withFile(
+        'netlify/functions/env-test.mjs',
+        `export default async (req, context) => Response.json({
+          NETLIFY_LOCAL: Netlify.env.get("NETLIFY_LOCAL"),
+          CONTEXT: Netlify.env.get("CONTEXT"),
+          MY_USER_VAR: Netlify.env.get("MY_USER_VAR"),
+        });
+        export const config = { path: "/env-test" };`,
+      )
+      .withStateFile({ siteId: 'site_id' })
+    const directory = await fixture.create()
+
+    // Test with injectUserEnv: false - only platform vars should be injected
+    const devWithoutUserEnv = new NetlifyDev({
+      projectRoot: directory,
+      environmentVariables: {
+        enabled: true,
+        injectUserEnv: false,
+      },
+      edgeFunctions: { enabled: false },
+      geolocation: { enabled: false },
+    })
+
+    await devWithoutUserEnv.start()
+    
+    const req1 = new Request('https://site.netlify/env-test')
+    const res1 = await devWithoutUserEnv.handle(req1)
+    const envVarsWithoutUserEnv = await res1?.json()
+
+    await devWithoutUserEnv.stop()
+
+    // Platform env vars should be present
+    expect(envVarsWithoutUserEnv).toHaveProperty('NETLIFY_LOCAL', 'true')
+    expect(envVarsWithoutUserEnv).toHaveProperty('CONTEXT', 'dev')
+    
+    // User-defined env vars should NOT be present
+    expect(envVarsWithoutUserEnv.MY_USER_VAR).toBeUndefined()
+
+    // Test with injectUserEnv: true (default) - all vars should be injected
+    const devWithUserEnv = new NetlifyDev({
+      projectRoot: directory,
+      environmentVariables: {
+        enabled: true,
+        injectUserEnv: true,
+      },
+      edgeFunctions: { enabled: false },
+      geolocation: { enabled: false },
+    })
+
+    await devWithUserEnv.start()
+
+    const req2 = new Request('https://site.netlify/env-test')
+    const res2 = await devWithUserEnv.handle(req2)
+    const envVarsWithUserEnv = await res2?.json()
+
+    await devWithUserEnv.stop()
+
+    // Both platform and user-defined env vars should be present
+    expect(envVarsWithUserEnv).toHaveProperty('NETLIFY_LOCAL', 'true')
+    expect(envVarsWithUserEnv).toHaveProperty('CONTEXT', 'dev')
+    expect(envVarsWithUserEnv).toHaveProperty('MY_USER_VAR', 'user value')
+
+    await fixture.destroy()
+  })
+})
diff --git a/packages/dev/src/main.ts b/packages/dev/src/main.ts
index e5818ee81..601c6c8c9 100644
--- a/packages/dev/src/main.ts
+++ b/packages/dev/src/main.ts
@@ -53,6 +53,15 @@ export interface Features {
    */
   environmentVariables?: {
     enabled?: boolean
+    /**
+     * Whether to inject user-defined environment variables from the linked site.
+     * When false, only platform environment variables (NETLIFY_LOCAL, CONTEXT, SITE_ID, etc.)
+     * are injected. When true, all environment variables including user-defined ones
+     * from Netlify UI, account, and config files are injected.
+     *
+     * {@default} true
+     */
+    injectUserEnv?: boolean
   }
 
   /**
@@ -181,6 +190,7 @@ export class NetlifyDev {
     blobs: boolean
     edgeFunctions: boolean
     environmentVariables: boolean
+    environmentVariablesInjectUserEnv: boolean
     functions: boolean
     geolocation: boolean
     headers: boolean
@@ -216,6 +226,7 @@ export class NetlifyDev {
       blobs: options.blobs?.enabled !== false,
       edgeFunctions: options.edgeFunctions?.enabled !== false,
       environmentVariables: options.environmentVariables?.enabled !== false,
+      environmentVariablesInjectUserEnv: options.environmentVariables?.injectUserEnv !== false,
       functions: options.functions?.enabled !== false,
       geolocation: options.geolocation?.enabled !== false,
       headers: options.headers?.enabled !== false,
@@ -517,6 +528,7 @@ export class NetlifyDev {
         accountSlug: config?.siteInfo?.account_slug,
         baseVariables: config?.env || {},
         envAPI: runtime.env,
+        injectUserEnv: this.#features.environmentVariablesInjectUserEnv,
         netlifyAPI: config?.api,
         siteID,
       })
diff --git a/packages/vite-plugin/README.md b/packages/vite-plugin/README.md
index 9e309cc9e..1518632f0 100644
--- a/packages/vite-plugin/README.md
+++ b/packages/vite-plugin/README.md
@@ -31,6 +31,11 @@ The plugin accepts the following options:
   same way as the Netlify production environment
 - `blobs`: Configure blob storage functionality
 - `edgeFunctions`: Configure edge functions
+- `environmentVariables`: Configure environment variable injection
+  - `enabled` (boolean, default: `true`): Enable environment variable injection
+  - `injectUserEnv` (boolean, default: `true`): Inject user-defined environment variables. When `false`, only platform
+    environment variables (like `NETLIFY_LOCAL`, `CONTEXT`, `SITE_ID`) are injected, excluding user-defined variables
+    from Netlify account settings, Netlify UI, config files, and addons
 - `functions`: Configure serverless functions
 - `headers`: Configure response headers
 - `images`: Configure Image CDN functionality
@@ -49,3 +54,27 @@ export default defineConfig({
   plugins: [netlify()],
 })
 ```
+
+### Environment Variables Configuration
+
+By default, the plugin injects all environment variables including user-defined ones from your Netlify site. If you want
+to only inject platform environment variables (useful for frameworks that manage their own environment variables):
+
+```js
+import { defineConfig } from 'vite'
+import netlify from '@netlify/vite-plugin'
+
+export default defineConfig({
+  plugins: [
+    netlify({
+      environmentVariables: {
+        enabled: true,
+        injectUserEnv: false,
+      },
+    }),
+  ],
+})
+```
+
+With `injectUserEnv: false`, only platform variables like `NETLIFY_LOCAL`, `CONTEXT`, and `SITE_ID` are injected,
+which are required for platform features like `purgeCache()` to work correctly.
diff --git a/packages/vite-plugin/src/main.test.ts b/packages/vite-plugin/src/main.test.ts
index 346cc3b67..a2ecba8a4 100644
--- a/packages/vite-plugin/src/main.test.ts
+++ b/packages/vite-plugin/src/main.test.ts
@@ -158,6 +158,61 @@ describe.for([['5.0.0'], ['6.0.0'], ['7.0.0']])('Vite %s', ([viteVersion]) => {
       await fixture.destroy()
     })
 
+    test('Populates platform env vars when injectUserEnv is false', async () => {
+      const fixture = new Fixture()
+        .withFile(
+          'vite.config.js',
+          `import { defineConfig } from 'vite';
+           import netlify from '@netlify/vite-plugin';
+
+           export default defineConfig({
+             plugins: [
+               netlify({ 
+                 middleware: false,
+                 environmentVariables: {
+                   enabled: true,
+                   injectUserEnv: false
+                 }
+               })
+             ]
+           });`,
+        )
+        .withFile(
+          'netlify.toml',
+          `[context.dev.environment]
+           MY_USER_VAR = "user value"`,
+        )
+        .withFile(
+          'index.html',
+          `<!DOCTYPE html>
+           <html>
+             <head><title>Hello World</title></head>
+             <body><h1>Hello from the browser</h1></body>
+           </html>`,
+        )
+      const directory = await fixture.create()
+      await fixture
+        .withPackages({
+          vite: viteVersion,
+          '@netlify/vite-plugin': pathToFileURL(path.resolve(directory, PLUGIN_PATH)).toString(),
+        })
+        .create()
+
+      const { server } = await startTestServer({
+        root: directory,
+      })
+
+      // Platform env vars should be present
+      expect(process.env).toHaveProperty('NETLIFY_LOCAL', 'true')
+      expect(process.env).toHaveProperty('CONTEXT', 'dev')
+      
+      // User-defined env vars should NOT be present when injectUserEnv is false
+      expect(process.env).not.toHaveProperty('MY_USER_VAR')
+
+      await server.close()
+      await fixture.destroy()
+    })
+
     test('Prints a basic message on server start', async () => {
       const fixture = new Fixture()
         .withFile(