Use Cloudflare Code Mode with Browser Run’s Chrome DevTools Protocol (CDP) connector when an AI model must inspect or operate a remote web page. Code Mode lets the model write one JavaScript program that calls typed MCP methods, loops over results, branches on page state and returns only the useful output. Browser Run supplies the remote browser session. They solve different parts of the problem: MCP exposes capabilities, Code Mode composes them, and CDP carries the browser interaction.
This guide also distinguishes that setup from @cloudflare/codemode/browser, which runs model-written code against tools inside a user’s own browser page and does not provide remote-browser control.
What Code Mode, MCP and Browser Run each do
Model Context Protocol (MCP)
MCP is the tool boundary. An MCP server publishes typed operations and schemas that a model can call. Your server or host remains responsible for authentication and authorization.
Code Mode
Without Code Mode, a model normally makes a tool call, receives the complete intermediate result, decides what to do next, and repeats. With Code Mode, it writes a small program against typed methods. The program can compose dependent calls, filter large responses, retry a safe read, loop through elements and return a compact result in one sandbox execution.
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Direct calls are still preferable for one simple action or a small, fixed tool set. Code Mode is most useful when the workflow has branching, iteration, progressive discovery or reusable logic.
Browser Run and CDP
Cloudflare describes Browser Run as a beta integration for inspecting and interacting with live pages through Chrome DevTools Protocol. Generated Code Mode executes against the browser session through the cdp connector. Browser Run is therefore the remote-browser path; Code Mode is the orchestration layer.
Choose an MCP design before writing code
| Design | Use it when | Trade-off |
|---|---|---|
One code tool |
Your existing MCP server has a manageable catalog. | Simple integration, but the model still needs a useful view of that catalog. |
search plus execute |
The API has many operations and schemas. | Progressive discovery reduces context size, at the cost of an additional discovery step. |
| Direct tool calls | One deterministic action or a few fixed calls. | Every intermediate result is exposed to the model. |
Cloudflare uses its large API MCP server as an example of the search-and-execute pattern. In a published comparison, Cloudflare reported 2,594 API tools requiring about 1,000 tokens with Code Mode, versus about 1,170,000 tokens for native full schemas and about 244,000 tokens for required parameters. Those are Cloudflare’s catalog figures, not a general benchmark.
Set up a remote browser workflow
- Create the Worker project and enable the current Code Mode runtime. Follow the current Cloudflare Code Mode and Browser Run documentation for package versions. The Browser Run examples configure a Browser binding and Worker Loader. The runtime must expose
CodemodeRuntime; the Vite plugin can generate that export automatically. - Attach Browser Run’s CDP connector. Your Code Mode host should make a typed
cdpclient available to generated code. Keep the browser session handle in the host, not in a prompt or tool result. - Choose session lifetime. A one-shot session is appropriate for an isolated inspection. Use a retained or durable session when a workflow must preserve login state, cookies or navigation between executions. Confirm the currently supported lifecycle in the Browser Run documentation because this beta surface can change.
- Expose only the operations the task needs. Typical methods include navigation, DOM inspection, element interaction, screenshots and evaluation of page state. Give each method a strict input schema and bounded output.
- Put authorization before side effects. Sandboxed code execution does not grant permission. Check the caller, target origin and requested action in the upstream handler or host callback before navigation, form submission, purchases, account changes or other external effects.
A Code Mode execution pattern
The following Worker-shaped example shows the control flow to implement with the current Cloudflare SDK. Method names and imports are intentionally kept at the connector boundary because Cloudflare marks Code Mode experimental and Browser Run beta; verify them against the versions you install.
export default {
async fetch(request, env) {
// Authenticate the caller before creating a browser session.
const input = await request.json();
if (input.origin !== "https://example.com") {
return new Response("origin not allowed", { status: 403 });
}
// The host creates a Browser Run session and exposes its typed CDP client.
const session = await env.BROWSER.createSession({
purpose: "read-only product check"
});
const cdp = session.cdp;
// This is the program Code Mode gives to the sandboxed runtime.
const result = await session.runCode(async (tools) => {
await tools.cdp.navigate({ url: input.url });
await tools.cdp.waitForNetworkIdle({ timeoutMs: 10000 });
const title = await tools.cdp.evaluate({
expression: "document.title"
});
const links = await tools.cdp.evaluate({
expression: "[...document.querySelectorAll('a')].slice(0, 20).map(a => ({text:a.innerText, href:a.href}))"
});
return {
title,
links: links.filter(link => link.text && link.href)
};
});
await session.close();
return Response.json(result);
}
};In production, replace the illustrative session methods with the current Browser Run connector API, validate input.url against an allowlist, cap navigation and evaluation time, and limit returned text. Never return cookies, authorization headers, page credentials or unrestricted DOM dumps to the model.
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Wrapping your own MCP server
For a small, existing tool catalog, Cloudflare’s single-tool pattern uses codeMcpServer(). The current guide says this returns an SDK v1 server and should be served with the explicit legacy createLegacyMcpHandler API. Treat both details as version-sensitive: pin compatible packages and re-check the guide before deployment.
// Illustrative structure; use the imports and adapter versions in the current guide.
const server = codeMcpServer({
tools: {
getPageText: async ({ url }) => {
await assertAllowedOrigin(url);
return browser.getPageText({ url });
},
clickAndRead: async ({ selector }) => {
await assertUserApproval("click", selector);
return browser.clickAndRead({ selector });
}
}
});
// Serve with the explicit legacy adapter required by the current SDK guide.
export default createLegacyMcpHandler(server);The important boundary is not the wrapper itself: every handler must enforce authorization, validate arguments and remove secrets from schemas and results.
Using search and execute for a large catalog
- Have the model search for the narrow capability it needs, such as browser navigation or accessibility-tree inspection.
- Return only matching operation names, descriptions and required arguments.
- Let Code Mode call those typed methods, compose their results and shape a small response.
- Reject unknown operations and enforce per-operation permissions in the executor.
This approach prevents a full API schema from consuming the model’s context and makes it easier to deny dangerous operations centrally.
Do not confuse remote automation with browser-owned tools
@cloudflare/codemode/browser is for tools owned by the visitor’s browser page. You define browser tools with schemas and implementations, construct createBrowserCodeTool() with an IframeSandboxExecutor, and execute the descriptor in the client. This is suitable for reading a page selection or local application state. It runs in a sandboxed iframe and does not control a remote browser.
Choose Browser Run when the target page must be opened and operated remotely. Choose the browser-owned integration when the capability or state already lives in the user’s own tab.
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Portal configuration
Cloudflare MCP portals can expose Code Mode through search and execution tools running in an isolated Dynamic Worker. The portal documentation describes the default policy as Opt-in; administrators can also disable the feature or enable it by default. For an opt-in portal, the documented connection form adds ?codemode=search_and_execute to the portal URL. Authentication and policy settings are administrator-specific, so inspect the account’s current configuration rather than assuming the default.
Security checklist for browser agents
- Authenticate the MCP caller before opening a session.
- Allowlist destination origins and block private-network targets unless explicitly required.
- Keep credentials in host bindings or secret storage; never place them in generated code, schemas or model-visible results.
- Require approval for writes, downloads, purchases, account changes and form submissions.
- Limit navigation count, script runtime, response size and screenshot dimensions.
- Redact cookies, tokens, passwords and personal data from logs.
- Close one-shot sessions and expire retained sessions deliberately.
- Pin package versions and test after Cloudflare updates because Code Mode is experimental and may introduce breaking changes.
Troubleshooting
The model can call tools but the page never changes
Check that the workflow uses Browser Run’s CDP connector, not @cloudflare/codemode/browser. Confirm a live browser session exists and that navigation is awaited before the next operation.
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Export it from the Worker runtime or enable the Vite plugin that supplies the export. Then rebuild and redeploy the Worker.
The adapter reports an SDK mismatch
codeMcpServer() currently returns an SDK v1 server in Cloudflare’s guide. Serve it with the documented createLegacyMcpHandler adapter and pin compatible package versions.
Results are too large or the model times out
Move loops and filtering into Code Mode, return only selected fields, cap DOM text and use search-before-execute for large catalogs. Set explicit navigation, network-idle and evaluation timeouts.
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A dangerous action was executed
Do not rely on the sandbox for permission. Add authorization and approval in the host callback or upstream tool handler, and remove side-effecting methods from read-only roles.
Do these 3 things before closing this tab:
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Check whether the run created a fresh one-shot session. Use the currently supported durable or retained lifecycle, persist the session identifier securely and handle expiry by re-authenticating.
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Frequently Asked Questions
Is Code Mode a browser automation library?
No. It is a model-to-tool execution pattern. Browser Run and its CDP connector provide the remote browser capabilities.
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When should I keep direct MCP calls?
Use direct calls for a simple, fixed operation where exposing the intermediate result is acceptable; use Code Mode for composition, loops, branching or discovery.
Can browser-owned Code Mode tools log in to a remote site?
No. The browser-owned integration runs inside the user’s page. Remote inspection and automation require Browser Run.
Is Cloudflare Code Mode production-stable?
Cloudflare labels Code Mode experimental and Browser Run beta. Verify current APIs and test upgrades before relying on them in production.
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The Bottom Line
For remote browser automation, combine Code Mode with Browser Run’s CDP connector, enforce authorization outside generated code, and select a one-shot or retained session deliberately. Use the browser-owned integration only for tools inside the visitor’s own page.
Quick Recap
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