diff --git a/packages/@aws-cdk/toolkit/lib/api/cloud-assembly/private/context-aware-source.ts b/packages/@aws-cdk/toolkit/lib/api/cloud-assembly/private/context-aware-source.ts
index dad63b05170be..60d9724fd6121 100644
--- a/packages/@aws-cdk/toolkit/lib/api/cloud-assembly/private/context-aware-source.ts
+++ b/packages/@aws-cdk/toolkit/lib/api/cloud-assembly/private/context-aware-source.ts
@@ -55,8 +55,8 @@ export class ContextAwareCloudAssembly implements ICloudAssemblySource {
    * Produce a Cloud Assembly, i.e. a set of stacks
    */
   public async produce(): Promise<cxapi.CloudAssembly> {
-    // We may need to run the cloud executable multiple times in order to satisfy all missing context
-    // (When the executable runs, it will tell us about context it wants to use
+    // We may need to run the cloud assembly source multiple times in order to satisfy all missing context
+    // (When the source producer runs, it will tell us about context it wants to use
     // but it missing. We'll then look up the context and run the executable again, and
     // again, until it doesn't complain anymore or we've stopped making progress).
     let previouslyMissingKeys: Set<string> | undefined;
@@ -82,7 +82,9 @@ export class ContextAwareCloudAssembly implements ICloudAssemblySource {
         previouslyMissingKeys = missingKeys;
 
         if (tryLookup) {
-          await this.ioHost.notify(debug('Some context information is missing. Fetching...'));
+          await this.ioHost.notify(debug('Some context information is missing. Fetching...', 'CDK_ASSEMBLY_I0241', {
+            missingKeys: Array.from(missingKeys),
+          }));
           await contextproviders.provideContextValues(
             assembly.manifest.missing,
             this.context,
@@ -90,6 +92,10 @@ export class ContextAwareCloudAssembly implements ICloudAssemblySource {
           );
 
           // Cache the new context to disk
+          await this.ioHost.notify(debug(`Writing updated context to ${this.contextFile}...`, 'CDK_ASSEMBLY_I0042', {
+            contextFile: this.contextFile,
+            context: this.context.all,
+          }));
           await this.context.save(this.contextFile);
 
           // Execute again
diff --git a/packages/@aws-cdk/toolkit/lib/api/cloud-assembly/private/prepare-source.ts b/packages/@aws-cdk/toolkit/lib/api/cloud-assembly/private/prepare-source.ts
index ba1715a105042..d7f5374edda66 100644
--- a/packages/@aws-cdk/toolkit/lib/api/cloud-assembly/private/prepare-source.ts
+++ b/packages/@aws-cdk/toolkit/lib/api/cloud-assembly/private/prepare-source.ts
@@ -169,6 +169,7 @@ export async function assemblyFromDirectory(assemblyDir: string, ioHost: ActionA
     throw err;
   }
 }
+
 function synthOptsDefaults(synthOpts: AppSynthOptions = {}): Settings {
   return new Settings({
     debug: false,
@@ -179,4 +180,3 @@ function synthOptsDefaults(synthOpts: AppSynthOptions = {}): Settings {
     ...synthOpts,
   }, true);
 }
-
diff --git a/packages/@aws-cdk/toolkit/lib/api/cloud-assembly/private/source-builder.ts b/packages/@aws-cdk/toolkit/lib/api/cloud-assembly/private/source-builder.ts
index 9fe3966d4c5a6..bcd2b4f807091 100644
--- a/packages/@aws-cdk/toolkit/lib/api/cloud-assembly/private/source-builder.ts
+++ b/packages/@aws-cdk/toolkit/lib/api/cloud-assembly/private/source-builder.ts
@@ -4,7 +4,7 @@ import { ContextAwareCloudAssembly, ContextAwareCloudAssemblyProps } from './con
 import { execInChildProcess } from './exec';
 import { assemblyFromDirectory, changeDir, determineOutputDirectory, guessExecutable, prepareDefaultEnvironment, withContext, withEnv } from './prepare-source';
 import { ToolkitServices } from '../../../toolkit/private';
-import { Context, ILock, RWLock } from '../../aws-cdk';
+import { Context, ILock, RWLock, Settings } from '../../aws-cdk';
 import { ToolkitError } from '../../errors';
 import { debug } from '../../io/private';
 import { AssemblyBuilder, CdkAppSourceProps } from '../source-builder';
@@ -28,7 +28,7 @@ export abstract class CloudAssemblySourceBuilder {
     props: CdkAppSourceProps = {},
   ): Promise<ICloudAssemblySource> {
     const services = await this.toolkitServices();
-    const context = new Context(); // @todo check if this needs to read anything
+    const context = new Context({ bag: new Settings(props.context ?? {}) });
     const contextAssemblyProps: ContextAwareCloudAssemblyProps = {
       services,
       context,
@@ -85,7 +85,8 @@ export abstract class CloudAssemblySourceBuilder {
    */
   public async fromCdkApp(app: string, props: CdkAppSourceProps = {}): Promise<ICloudAssemblySource> {
     const services: ToolkitServices = await this.toolkitServices();
-    const context = new Context(); // @todo this definitely needs to read files
+    // @todo this definitely needs to read files from the CWD
+    const context = new Context({ bag: new Settings(props.context ?? {}) });
     const contextAssemblyProps: ContextAwareCloudAssemblyProps = {
       services,
       context,
diff --git a/packages/@aws-cdk/toolkit/lib/api/cloud-assembly/source-builder.ts b/packages/@aws-cdk/toolkit/lib/api/cloud-assembly/source-builder.ts
index 24f091846da81..9f87860ad30d8 100644
--- a/packages/@aws-cdk/toolkit/lib/api/cloud-assembly/source-builder.ts
+++ b/packages/@aws-cdk/toolkit/lib/api/cloud-assembly/source-builder.ts
@@ -19,6 +19,8 @@ export type AssemblyBuilder = (props: AppProps) => Promise<cxapi.CloudAssembly>;
  */
 export interface CdkAppSourceProps {
   /**
+   * Execute the application in this working directory.
+   *
    * @default - current working directory
    */
   readonly workingDirectory?: string;
@@ -39,6 +41,17 @@ export interface CdkAppSourceProps {
    */
   readonly lookups?: boolean;
 
+  /**
+   * Context values for the application.
+   *
+   * Context can be read in the app from any construct using `node.getContext(key)`.
+   *
+   * @default - no context
+   */
+  readonly context?: {
+    [key: string]: any;
+  };
+
   /**
    * Options that are passed through the context to a CDK app on synth
    */
diff --git a/packages/@aws-cdk/toolkit/test/_fixtures/external-context/app.js b/packages/@aws-cdk/toolkit/test/_fixtures/external-context/app.js
new file mode 100644
index 0000000000000..fdc4cb2a166f5
--- /dev/null
+++ b/packages/@aws-cdk/toolkit/test/_fixtures/external-context/app.js
@@ -0,0 +1,9 @@
+import * as s3 from 'aws-cdk-lib/aws-s3';
+import * as core from 'aws-cdk-lib/core';
+
+const app = new core.App();
+const stack = new core.Stack(app, 'Stack1');
+new s3.Bucket(stack, 'MyBucket', {
+    bucketName: app.node.tryGetContext('externally-provided-bucket-name')
+});
+app.synth();
diff --git a/packages/@aws-cdk/toolkit/test/_fixtures/external-context/index.ts b/packages/@aws-cdk/toolkit/test/_fixtures/external-context/index.ts
new file mode 100644
index 0000000000000..5f505989fcde6
--- /dev/null
+++ b/packages/@aws-cdk/toolkit/test/_fixtures/external-context/index.ts
@@ -0,0 +1,11 @@
+import * as s3 from 'aws-cdk-lib/aws-s3';
+import * as core from 'aws-cdk-lib/core';
+
+export default async () => {
+  const app = new core.App();
+  const stack = new core.Stack(app, 'Stack1');
+  new s3.Bucket(stack, 'MyBucket', {
+    bucketName: app.node.tryGetContext('externally-provided-bucket-name'),
+  });
+  return app.synth() as any;
+};
diff --git a/packages/@aws-cdk/toolkit/test/_helpers/index.ts b/packages/@aws-cdk/toolkit/test/_helpers/index.ts
index c619ee3c7919f..e854951701c69 100644
--- a/packages/@aws-cdk/toolkit/test/_helpers/index.ts
+++ b/packages/@aws-cdk/toolkit/test/_helpers/index.ts
@@ -9,7 +9,7 @@ function fixturePath(...parts: string[]): string {
   return path.normalize(path.join(__dirname, '..', '_fixtures', ...parts));
 }
 
-export async function appFixture(toolkit: Toolkit, name: string) {
+export async function appFixture(toolkit: Toolkit, name: string, context?: { [key: string]: any }) {
   const appPath = fixturePath(name, 'app.js');
   if (!fs.existsSync(appPath)) {
     throw new Error(`App Fixture ${name} does not exist in ${appPath}`);
@@ -17,14 +17,16 @@ export async function appFixture(toolkit: Toolkit, name: string) {
   const app = `cat ${appPath} | node --input-type=module`;
   return toolkit.fromCdkApp(app, {
     outdir: determineOutputDirectory(),
+    context,
   });
 }
 
-export function builderFixture(toolkit: Toolkit, name: string) {
+export function builderFixture(toolkit: Toolkit, name: string, context?: { [key: string]: any }) {
   // eslint-disable-next-line @typescript-eslint/no-require-imports
   const builder = require(path.join(__dirname, '..', '_fixtures', name)).default;
   return toolkit.fromAssemblyBuilder(builder, {
     outdir: determineOutputDirectory(),
+    context,
   });
 }
 
diff --git a/packages/@aws-cdk/toolkit/test/api/cloud-assembly/source-builder.test.ts b/packages/@aws-cdk/toolkit/test/api/cloud-assembly/source-builder.test.ts
index 9e5ec588963c4..a69c4992591e2 100644
--- a/packages/@aws-cdk/toolkit/test/api/cloud-assembly/source-builder.test.ts
+++ b/packages/@aws-cdk/toolkit/test/api/cloud-assembly/source-builder.test.ts
@@ -12,32 +12,53 @@ describe('fromAssemblyBuilder', () => {
   test('defaults', async () => {
     // WHEN
     const cx = await builderFixture(toolkit, 'two-empty-stacks');
-    const cached = await toolkit.synth(cx);
-    const assembly = await cached.produce();
+    const assembly = await cx.produce();
 
     // THEN
     expect(assembly.stacksRecursively.map(s => s.hierarchicalId)).toEqual(['Stack1', 'Stack2']);
   });
+
+  test('can provide context', async () => {
+    // WHEN
+    const cx = await builderFixture(toolkit, 'external-context', {
+      'externally-provided-bucket-name': 'amzn-s3-demo-bucket',
+    });
+    const assembly = await cx.produce();
+    const stack = assembly.getStackByName('Stack1').template;
+
+    // THEN
+    expect(JSON.stringify(stack)).toContain('amzn-s3-demo-bucket');
+  });
 });
 
-describe('fromAssemblyDirectory', () => {
+describe('fromCdkApp', () => {
   test('defaults', async () => {
     // WHEN
-    const cx = await cdkOutFixture(toolkit, 'two-empty-stacks');
-    const cached = await toolkit.synth(cx);
-    const assembly = await cached.produce();
+    const cx = await appFixture(toolkit, 'two-empty-stacks');
+    const assembly = await cx.produce();
 
     // THEN
     expect(assembly.stacksRecursively.map(s => s.hierarchicalId)).toEqual(['Stack1', 'Stack2']);
   });
+
+  test('can provide context', async () => {
+    // WHEN
+    const cx = await appFixture(toolkit, 'external-context', {
+      'externally-provided-bucket-name': 'amzn-s3-demo-bucket',
+    });
+    const assembly = await cx.produce();
+    const stack = assembly.getStackByName('Stack1').template;
+
+    // THEN
+    expect(JSON.stringify(stack)).toContain('amzn-s3-demo-bucket');
+  });
 });
 
-describe('fromCdkApp', () => {
+describe('fromAssemblyDirectory', () => {
   test('defaults', async () => {
     // WHEN
-    const cx = await appFixture(toolkit, 'two-empty-stacks');
-    const cached = await toolkit.synth(cx);
-    const assembly = await cached.produce();
+    const cx = await cdkOutFixture(toolkit, 'two-empty-stacks');
+    const assembly = await cx.produce();
 
     // THEN
     expect(assembly.stacksRecursively.map(s => s.hierarchicalId)).toEqual(['Stack1', 'Stack2']);