diff --git a/src/LineWriterImpl.ts b/src/InMemoryLineWriter.ts
similarity index 95%
rename from src/LineWriterImpl.ts
rename to src/InMemoryLineWriter.ts
index 249f6727..19e12ffc 100644
--- a/src/LineWriterImpl.ts
+++ b/src/InMemoryLineWriter.ts
@@ -16,7 +16,7 @@
 
 import { LineWriter } from './LineWriter.js';
 
-export class LineWriterImpl implements LineWriter {
+export class InMemoryLineWriter implements LineWriter {
   #indentation: string;
   #currentIndentation = 0;
   #lines: string[] = [];
diff --git a/src/stringify.ts b/src/stringify.ts
index 2dbe9888..63980634 100644
--- a/src/stringify.ts
+++ b/src/stringify.ts
@@ -14,13 +14,15 @@
     limitations under the License.
  */
 
-import { LineWriterImpl } from './LineWriterImpl.js';
+import { InMemoryLineWriter } from './InMemoryLineWriter.js';
+import { LineWriter } from './LineWriter.js';
 import { PuppeteerStringifyExtension } from './PuppeteerStringifyExtension.js';
 import type { Step, UserFlow } from './Schema.js';
 import { StringifyExtension } from './StringifyExtension.js';
 
 export interface StringifyOptions {
   extension?: StringifyExtension;
+  writer?: LineWriter;
   indentation?: string;
 }
 
@@ -39,15 +41,8 @@ export async function stringify(
   if (!opts) {
     opts = {};
   }
-  let ext = opts.extension;
-  if (!ext) {
-    ext = new PuppeteerStringifyExtension();
-  }
-
-  if (!opts.indentation) {
-    opts.indentation = '  ';
-  }
-  const out = new LineWriterImpl(opts.indentation);
+  const ext = opts.extension ?? new PuppeteerStringifyExtension();
+  const out = opts.writer ?? new InMemoryLineWriter(opts.indentation ?? '  ');
 
   await ext.beforeAllSteps?.(out, flow);
   for (const step of flow.steps) {
@@ -80,7 +75,7 @@ export async function stringifyStep(
   if (!opts.indentation) {
     opts.indentation = '  ';
   }
-  const out = new LineWriterImpl(opts.indentation);
+  const out = new InMemoryLineWriter(opts.indentation);
 
   await ext.beforeEachStep?.(out, step);
   await ext.stringifyStep(out, step);
diff --git a/test/LineWriterImpl_test.ts b/test/InMemoryLineWriter_test.ts
similarity index 85%
rename from test/LineWriterImpl_test.ts
rename to test/InMemoryLineWriter_test.ts
index 652b97d2..52241123 100644
--- a/test/LineWriterImpl_test.ts
+++ b/test/InMemoryLineWriter_test.ts
@@ -14,12 +14,12 @@
     limitations under the License.
  */
 
-import { LineWriterImpl } from '../src/LineWriterImpl.js';
+import { InMemoryLineWriter } from '../src/InMemoryLineWriter.js';
 import { assert } from 'chai';
 
-describe('LineWriterImpl', () => {
+describe('InMemoryLineWriter', () => {
   it('should open and close blocks', () => {
-    const out = new LineWriterImpl('  ');
+    const out = new InMemoryLineWriter('  ');
     out.appendLine('{').startBlock();
     out.appendLine('console.log("test");');
     out.endBlock().appendLine('}');
diff --git a/test/PuppeteerStringifyExtension_test.ts b/test/PuppeteerStringifyExtension_test.ts
index 27bc4253..5df97a2c 100644
--- a/test/PuppeteerStringifyExtension_test.ts
+++ b/test/PuppeteerStringifyExtension_test.ts
@@ -15,7 +15,7 @@
  */
 
 import snapshot from 'snap-shot-it';
-import { LineWriterImpl } from '../src/LineWriterImpl.js';
+import { InMemoryLineWriter } from '../src/InMemoryLineWriter.js';
 import { PuppeteerStringifyExtension } from '../src/PuppeteerStringifyExtension.js';
 
 describe('PuppeteerStringifyExtension', () => {
@@ -31,7 +31,7 @@ describe('PuppeteerStringifyExtension', () => {
     };
     const flow = { title: 'test', steps: [step] };
 
-    const writer = new LineWriterImpl('  ');
+    const writer = new InMemoryLineWriter('  ');
     await ext.stringifyStep(writer, step, flow);
     snapshot(writer.toString());
   });
@@ -47,7 +47,7 @@ describe('PuppeteerStringifyExtension', () => {
     };
     const flow = { title: 'test', steps: [step] };
 
-    const writer = new LineWriterImpl('  ');
+    const writer = new InMemoryLineWriter('  ');
     await ext.stringifyStep(writer, step, flow);
     snapshot(writer.toString());
   });
@@ -62,7 +62,7 @@ describe('PuppeteerStringifyExtension', () => {
     };
     const flow = { title: 'test', steps: [step] };
 
-    const writer = new LineWriterImpl('  ');
+    const writer = new InMemoryLineWriter('  ');
     await ext.stringifyStep(writer, step, flow);
     snapshot(writer.toString());
   });
@@ -76,7 +76,7 @@ describe('PuppeteerStringifyExtension', () => {
     };
     const flow = { title: 'test', steps: [step] };
 
-    const writer = new LineWriterImpl('  ');
+    const writer = new InMemoryLineWriter('  ');
     await ext.stringifyStep(writer, step, flow);
     snapshot(writer.toString());
   });
@@ -90,7 +90,7 @@ describe('PuppeteerStringifyExtension', () => {
     };
     const flow = { title: 'test', steps: [step] };
 
-    const writer = new LineWriterImpl('  ');
+    const writer = new InMemoryLineWriter('  ');
     await ext.stringifyStep(writer, step, flow);
     snapshot(writer.toString());
   });