diff --git a/sdk/typescript/tests/multimodal_comprehensive.test.ts b/sdk/typescript/tests/multimodal_comprehensive.test.ts
new file mode 100644
index 000000000..70c10d56e
--- /dev/null
+++ b/sdk/typescript/tests/multimodal_comprehensive.test.ts
@@ -0,0 +1,215 @@
+import { afterEach, describe, expect, it, vi } from 'vitest';
+import { mkdtemp, rm, writeFile } from 'node:fs/promises';
+import { tmpdir } from 'node:os';
+import { join } from 'node:path';
+
+import {
+  Audio,
+  File,
+  Image,
+  Text,
+  audioFromFile,
+  audioFromUrl,
+  fileFromPath,
+  imageFromBuffer,
+  imageFromFile,
+  text,
+} from '../src/index.js';
+
+describe('multimodal helpers comprehensive coverage', () => {
+  let tempDir: string | null = null;
+
+  async function writeFixture(filename: string, contents: Uint8Array): Promise<string> {
+    tempDir ??= await mkdtemp(join(tmpdir(), 'agentfield-multimodal-comprehensive-'));
+    const filePath = join(tempDir, filename);
+    await writeFile(filePath, contents);
+    return filePath;
+  }
+
+  afterEach(async () => {
+    vi.unstubAllGlobals();
+    vi.restoreAllMocks();
+    if (tempDir) {
+      await rm(tempDir, { recursive: true, force: true });
+      tempDir = null;
+    }
+  });
+
+  it('constructs text content without changing its value', () => {
+    const direct = new Text('  hello\nworld  ');
+    const fromHelper = text('');
+
+    expect(direct).toBeInstanceOf(Text);
+    expect(direct).toEqual({ type: 'text', text: '  hello\nworld  ' });
+    expect(fromHelper).toEqual({ type: 'text', text: '' });
+  });
+
+  it('imageFromFile encodes image bytes with a case-insensitive MIME type', async () => {
+    const bytes = Uint8Array.from([0x89, 0x50, 0x4e, 0x47]);
+    const filePath = await writeFixture('sample.PNG', bytes);
+
+    const image = await imageFromFile(filePath, 'auto');
+
+    expect(image).toBeInstanceOf(Image);
+    expect(image.type).toBe('image_url');
+    expect(image.imageUrl).toEqual({
+      url: `data:image/png;base64,${Buffer.from(bytes).toString('base64')}`,
+      detail: 'auto',
+    });
+  });
+
+  it('Image.fromFile falls back to JPEG and high detail for an unknown extension', async () => {
+    const bytes = Uint8Array.from([1, 2, 3, 4]);
+    const filePath = await writeFixture('sample.unknown', bytes);
+
+    const image = await Image.fromFile(filePath);
+
+    expect(image.imageUrl).toEqual({
+      url: `data:image/jpeg;base64,${Buffer.from(bytes).toString('base64')}`,
+      detail: 'high',
+    });
+  });
+
+  it('creates images from buffers, base64, and URLs', async () => {
+    const bufferImage = await imageFromBuffer(Uint8Array.from([1, 2, 3]), 'image/webp', 'low');
+    const base64Image = await Image.fromBase64('AQID');
+    const urlImage = Image.fromUrl('https://example.com/image.png', 'auto');
+
+    expect(bufferImage.imageUrl).toEqual({
+      url: 'data:image/webp;base64,AQID',
+      detail: 'low',
+    });
+    expect(base64Image.imageUrl).toEqual({
+      url: 'data:image/jpeg;base64,AQID',
+      detail: 'high',
+    });
+    expect(urlImage.imageUrl).toEqual({
+      url: 'https://example.com/image.png',
+      detail: 'auto',
+    });
+  });
+
+  it('Audio.fromBuffer creates input_audio content and honors the requested format', async () => {
+    const bytes = Uint8Array.from([4, 5, 6]);
+
+    const audio = await Audio.fromBuffer(bytes, 'flac');
+
+    expect(audio).toBeInstanceOf(Audio);
+    expect(audio.type).toBe('input_audio');
+    expect(audio.audio).toEqual({
+      data: Buffer.from(bytes).toString('base64'),
+      format: 'flac',
+    });
+  });
+
+  it('Audio.fromBase64 preserves data and defaults to WAV', async () => {
+    const audio = await Audio.fromBase64('BAUG');
+
+    expect(audio.audio).toEqual({ data: 'BAUG', format: 'wav' });
+  });
+
+  it('audioFromFile round-trips bytes and detects an uppercase extension', async () => {
+    const bytes = Uint8Array.from([0x49, 0x44, 0x33, 0x04]);
+    const filePath = await writeFixture('sample.MP3', bytes);
+
+    const audio = await audioFromFile(filePath);
+
+    expect(audio).toBeInstanceOf(Audio);
+    expect(audio.audio).toEqual({
+      data: Buffer.from(bytes).toString('base64'),
+      format: 'mp3',
+    });
+  });
+
+  it('Audio.fromFile uses WAV for unknown extensions unless a format is supplied', async () => {
+    const bytes = Uint8Array.from([7, 8, 9]);
+    const filePath = await writeFixture('sample.aac', bytes);
+
+    const fallback = await Audio.fromFile(filePath);
+    const explicit = await Audio.fromFile(filePath, 'ogg');
+
+    expect(fallback.audio).toEqual({
+      data: Buffer.from(bytes).toString('base64'),
+      format: 'wav',
+    });
+    expect(explicit.audio).toEqual({
+      data: Buffer.from(bytes).toString('base64'),
+      format: 'ogg',
+    });
+  });
+
+  it('audioFromUrl fetches audio bytes and converts them to base64', async () => {
+    const bytes = Uint8Array.from([10, 11, 12]);
+    const fetchMock = vi.fn(async () => new Response(bytes, { status: 200 }));
+    vi.stubGlobal('fetch', fetchMock);
+
+    const audio = await audioFromUrl('https://example.com/audio.ogg', 'ogg');
+
+    expect(fetchMock).toHaveBeenCalledOnce();
+    expect(fetchMock).toHaveBeenCalledWith('https://example.com/audio.ogg');
+    expect(audio.audio).toEqual({
+      data: Buffer.from(bytes).toString('base64'),
+      format: 'ogg',
+    });
+  });
+
+  it('Audio.fromUrl defaults to WAV', async () => {
+    const bytes = Uint8Array.from([10, 11, 12]);
+    const fetchMock = vi.fn(async () => new Response(bytes, { status: 200 }));
+    vi.stubGlobal('fetch', fetchMock);
+
+    const audio = await Audio.fromUrl('https://example.com/audio.wav');
+
+    expect(fetchMock).toHaveBeenCalledOnce();
+    expect(fetchMock).toHaveBeenCalledWith('https://example.com/audio.wav');
+    expect(audio.audio).toEqual({
+      data: Buffer.from(bytes).toString('base64'),
+      format: 'wav',
+    });
+  });
+
+  it('Audio.fromUrl reports unsuccessful HTTP responses', async () => {
+    vi.stubGlobal(
+      'fetch',
+      vi.fn(async () => new Response(null, { status: 503, statusText: 'Service Unavailable' }))
+    );
+
+    await expect(Audio.fromUrl('https://example.com/unavailable.wav')).rejects.toThrow(
+      'Failed to fetch audio from URL: 503 Service Unavailable'
+    );
+  });
+
+  it('Audio.fromUrl normalizes fetch TypeErrors and preserves other failures', async () => {
+    const otherFailure = new Error('connection closed');
+    const fetchMock = vi
+      .fn()
+      .mockRejectedValueOnce(new TypeError('fetch failed'))
+      .mockRejectedValueOnce(otherFailure);
+    vi.stubGlobal('fetch', fetchMock);
+
+    await expect(Audio.fromUrl('https://example.com/network.wav')).rejects.toThrow(
+      'URL download requires a fetch-compatible environment'
+    );
+    await expect(Audio.fromUrl('https://example.com/error.wav')).rejects.toBe(otherFailure);
+  });
+
+  it.each([
+    ['report.pdf', 'application/pdf'],
+    ['report.DOCX', 'application/vnd.openxmlformats-officedocument.wordprocessingml.document'],
+    ['image.png', 'image/png'],
+    ['audio.MP3', 'audio/mpeg'],
+    ['README', 'application/octet-stream'],
+  ])('infers %s as %s when creating generic file content', async (filename, mimeType) => {
+    const bytes = Uint8Array.from([13, 14, 15]);
+    const filePath = await writeFixture(filename, bytes);
+
+    const file = await fileFromPath(filePath);
+
+    expect(file).toBeInstanceOf(File);
+    expect(file.type).toBe('file');
+    expect(file.file).toEqual({
+      url: `data:${mimeType};base64,${Buffer.from(bytes).toString('base64')}`,
+      mimeType,
+    });
+  });
+});