diff --git a/packages/opencode/test/tool/webfetch.test.ts b/packages/opencode/test/tool/webfetch.test.ts
index 088f3dd16d..00e9dcc96c 100644
--- a/packages/opencode/test/tool/webfetch.test.ts
+++ b/packages/opencode/test/tool/webfetch.test.ts
@@ -17,30 +17,25 @@ const ctx = {
   ask: async () => {},
 }
 
-async function withFetch(
-  mockFetch: (input: string | URL | Request, init?: RequestInit) => Promise<Response>,
-  fn: () => Promise<void>,
-) {
-  const originalFetch = globalThis.fetch
-  globalThis.fetch = mockFetch as unknown as typeof fetch
-  try {
-    await fn()
-  } finally {
-    globalThis.fetch = originalFetch
-  }
+async function withFetch(fetch: (req: Request) => Response | Promise<Response>, fn: (url: URL) => Promise<void>) {
+  using server = Bun.serve({ port: 0, fetch })
+  await fn(server.url)
 }
 
 describe("tool.webfetch", () => {
   test("returns image responses as file attachments", async () => {
     const bytes = new Uint8Array([137, 80, 78, 71, 13, 10, 26, 10])
     await withFetch(
-      async () => new Response(bytes, { status: 200, headers: { "content-type": "IMAGE/PNG; charset=binary" } }),
-      async () => {
+      () => new Response(bytes, { status: 200, headers: { "content-type": "IMAGE/PNG; charset=binary" } }),
+      async (url) => {
         await Instance.provide({
           directory: projectRoot,
           fn: async () => {
             const webfetch = await WebFetchTool.init()
-            const result = await webfetch.execute({ url: "https://example.com/image.png", format: "markdown" }, ctx)
+            const result = await webfetch.execute(
+              { url: new URL("/image.png", url).toString(), format: "markdown" },
+              ctx,
+            )
             expect(result.output).toBe("Image fetched successfully")
             expect(result.attachments).toBeDefined()
             expect(result.attachments?.length).toBe(1)
@@ -59,17 +54,17 @@ describe("tool.webfetch", () => {
   test("keeps svg as text output", async () => {
     const svg = '<svg xmlns="http://www.w3.org/2000/svg"><text>hello</text></svg>'
     await withFetch(
-      async () =>
+      () =>
         new Response(svg, {
           status: 200,
           headers: { "content-type": "image/svg+xml; charset=UTF-8" },
         }),
-      async () => {
+      async (url) => {
         await Instance.provide({
           directory: projectRoot,
           fn: async () => {
             const webfetch = await WebFetchTool.init()
-            const result = await webfetch.execute({ url: "https://example.com/image.svg", format: "html" }, ctx)
+            const result = await webfetch.execute({ url: new URL("/image.svg", url).toString(), format: "html" }, ctx)
             expect(result.output).toContain("<svg")
             expect(result.attachments).toBeUndefined()
           },
@@ -80,17 +75,17 @@ describe("tool.webfetch", () => {
 
   test("keeps text responses as text output", async () => {
     await withFetch(
-      async () =>
+      () =>
         new Response("hello from webfetch", {
           status: 200,
           headers: { "content-type": "text/plain; charset=utf-8" },
         }),
-      async () => {
+      async (url) => {
         await Instance.provide({
           directory: projectRoot,
           fn: async () => {
             const webfetch = await WebFetchTool.init()
-            const result = await webfetch.execute({ url: "https://example.com/file.txt", format: "text" }, ctx)
+            const result = await webfetch.execute({ url: new URL("/file.txt", url).toString(), format: "text" }, ctx)
             expect(result.output).toBe("hello from webfetch")
             expect(result.attachments).toBeUndefined()
           },