brapper

brapper — browser app wrapper — framework for building MCP/HTTP API wrappers around browser-based web applications.

Each project built with brapper is a brap — a browser app wrap — a disposable adapter that wraps one specific web app and exposes it as an API.

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The internet wasn't built for agents. Yet.

AI agents are here. They reason, plan, and act. But the internet they're trying to act on was built for humans — login screens, CAPTCHAs, JavaScript-rendered UIs, and zero machine-readable APIs for most of its surface area.

The gap is real: millions of useful web applications have no API. No MCP endpoint. No way for an agent to just call them. You either reverse-engineer private APIs (fragile, breaks on every deploy) or you give up and do it manually.

brapper is the bridge for this transition era.

Attach to a real browser running the app, expose its functionality as MCP + HTTP, and let your agents use it today — without reverse-engineering or reimplementing anything. The browser does all the work; brapper just orchestrates it.

Projects built with brapper are called braps — pragmatic adapters for the pre-agent web. Each one is a thin layer meant to become unnecessary. When the web catches up and apps start shipping native MCP support, you won't need your brap anymore. Until then: wrap it, ship it, move on.

brapper and braps are not forever solutions — they are the scaffolding that gets us from here to there.

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Core concepts

The problem it solves

Many web applications have rich functionality accessible only through their UI, with no public API. Building integrations means either:

• Reverse-engineering their private APIs (fragile, needs maintenance)
• Using a real browser and automating it (robust, uses the app as intended)

Brapper takes the second path and provides the infrastructure to do it cleanly and consistently across projects.

The brapper project (a "brap")

A project built with brapper is called a brap. Each brap is a standalone npm package that:

1. Contains an App class — the core adapter for one specific target web app (MyApp, etc.)
2. Exposes an HTTP API server (REST + optional HTTP MCP) for network access
3. Optionally ships an MCP stdio binary for direct AI agent integration (Cursor, Claude Desktop)
4. Exports a typed client (MyClient, etc.) so other projects can consume the API with full TypeScript types

@my-org/app-one-brap   # a brap: wraps app-one.example.com
@my-org/app-two-brap   # a brap: wraps app-two.example.com

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Architecture

┌─────────────────────────────────────────────────────────┐
│                        brap project                     │
│                                                         │
│   ┌─────────────┐      ┌────────────────────────────┐   │
│   │   MyApp     │─────▶│    HTTP API Server         │   │
│   │  (adapter)  │      │  (Hono routes + MCP HTTP)  │   │
│   │             │      └────────────────────────────┘   │
│   │  - session  │      ┌────────────────────────────┐   │
│   │  - warmUp   │      │    MCP stdio binary        │   │
│   │  - methods  │      │ (npx @my-org/my-brap-mcp)  │   │
│   └──────┬──────┘      └────────────────────────────┘   │
│          │                                              │
│   ┌──────▼──────┐                                       │
│   │  Browser    │   Chrome with remote debugging        │
│   │  Session    │   (CDP / puppeteer-core)              │
│   └─────────────┘                                       │
└─────────────────────────────────────────────────────────┘

Two deployment targets from one project

Every brap can produce two separate runnable artifacts:

Artifact	Entry point	How it runs	Purpose
HTTP server	src/server.ts	Docker / process	REST API + HTTP MCP
MCP stdio	src/mcp.ts	npx locally	AI agent integration

The stdio MCP is a smart local client to the HTTP server. It has access to the local filesystem (can read files by path), composes multiple HTTP calls into high-level tools, and is configured in Cursor/Claude Desktop via mcpServers.

// .cursor/mcp.json
{
  "mcpServers": {
    "my-brap": {
      "command": "npx",
      "args": ["-y", "@my-org/my-brap-mcp"],
      "env": { "SERVER_URL": "https://my-brap.example.com", "AUTH_TOKEN": "secret" }
    }
  }
}

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The App class pattern

The App class is the heart of each brap. It encapsulates everything specific to one target web application: browser setup, warm-up, authentication, and all scraping/automation methods.

// In @my-org/my-brap
export class MyApp {
  constructor(private worker: PageWorker) {}

  static async create(worker: PageWorker): Promise<MyApp> {
    await worker.injectScript(customHookSource)
    await worker.page.goto('https://target.example.com')
    await waitForLogin(worker)
    return new MyApp(worker)
  }

  async listItems(params?: ListParams) {
    return this.worker.evaluateExpression('window.__api.listItems(...)')
  }

  async createItem(payload: ItemPayload) { ... }
  async uploadFile(path: string) { ... }
}

Concurrency and the instance pool

Each HTTP request can spin up a separate MyApp instance on its own browser tab, run its task, and release. BrowserSession manages the pool with a configurable concurrency limit and a queue for excess requests:

// In server route
app.post('/v1/items', async (c) => {
  return session.withApp(MyApp, async (app) => {
    const result = await app.createItem(body)
    return c.json(result)
  })
})

withApp handles:

• acquiring a tab from the pool (waiting in queue if all are busy)
• creating the App instance on that tab
• releasing the tab back to the pool after the handler completes (or throws)

// BrowserSession config
const session = new BrowserSession({
  wsEndpoint: env.BROWSER_WS_ENDPOINT,
  concurrency: 3,          // up to 3 parallel tabs
  queueTimeout: 30_000,    // reject if waiting > 30s
})

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Type-safe HTTP client via Hono RPC

Routes defined in the server are automatically available as a typed client — no code generation step:

// @my-org/my-brap/src/http/routes.ts
const app = new Hono()
  .post('/items', ...)
  .get('/items', ...)

export type AppType = typeof app

// @my-org/my-brap/src/client/MyClient.ts
import { hc } from 'brapper'
import type { AppType } from '../http/routes.js'

export class MyClient {
  private rpc = hc<AppType>(this.serverUrl, {
    headers: { Authorization: `Bearer ${this.token}` },
  })

  constructor(private serverUrl: string, private token: string) {}

  async createItem(payload: ItemPayload) {
    const res = await this.rpc.items.$post({ json: payload })
    return res.json()
  }
}

Consumer:

import { MyClient } from '@my-org/my-brap'

const client = new MyClient('https://my-brap.example.com', process.env.AUTH_TOKEN)
const item = await client.createItem({ title: 'Hello' })

Full autocomplete, typed responses, zero maintenance overhead.

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Binary files

Brapper's approach to binary data:

• HTTP API: handles multipart uploads and binary responses natively — this is where files belong
• MCP tools (both HTTP and stdio): return fileId / URL references, not raw binary
• MCP stdio has the unique advantage of filesystem access — tools accept a local path, read the file, and POST it to the HTTP API

// MCP stdio tool
server.tool('upload_file', { path: z.string() }, async ({ path }) => {
  const bytes = await fs.readFile(path)
  const { fileId } = await client.post('/v1/upload', bytes)
  return { content: [{ type: 'text', text: fileId }] }
})

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What brapper provides

Module	Export	Purpose
browser/BrowserSession	BrowserSession	CDP connection, reconnect, withPage, withApp, openPage, applyCookies
browser/PageWorker	PageWorker	browserFetch, waitForResponse, onResponse, injectScript, evaluate
http/createApp	createApp	Base Hono app: CORS, auth, /health, error shape
mcp/createMcpServer	createMcpHandler	HTTP MCP factory
config/parseEnv	parseEnv, baseEnvSchema	Zod env parsing + WS endpoint resolution
logging/createLogger	createLogger	pino + pino-pretty in dev
createBrap	createBrap	Top-level orchestrator: connect → cookies → warm-up → serve
—	hc (re-export from hono/client)	Hono RPC typed client factory
—	z (re-export from zod)	Extend baseEnvSchema in brap configs
—	Logger, Hono (type re-exports)	Type-only convenience imports

Coming in v0.2–v0.3: SessionGate, SessionMonitor, RecoveryStrategy, createStdioApp, HttpClient, stdioBaseEnvSchema

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What brapper does NOT provide

• Target-specific logic (selectors, URLs, auth flows, scraping patterns)
• Captcha solver implementations (strategy interface is provided; implementations live in brap)
• Any knowledge of specific web applications

All of that lives in each individual brap project.

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Project layout of a brap

@my-org/my-brap/
├── src/
│   ├── server.ts              # HTTP server entry point
│   ├── mcp.ts                 # stdio MCP entry point (#!/usr/bin/env node)
│   ├── config.ts              # Zod env schema (extends baseEnvSchema)
│   ├── app/
│   │   └── MyApp.ts           # the App class — all target-specific logic
│   ├── http/
│   │   └── routes.ts          # Hono routes + export type AppType
│   ├── mcp/
│   │   ├── http-tools.ts      # thin MCP tools for HTTP transport
│   │   └── stdio-tools.ts     # rich MCP tools for stdio (filesystem access)
│   └── client/
│       └── MyClient.ts        # typed client (hc<AppType> wrapper)
├── index.ts                   # export { MyClient, MyApp }
├── deploy/
│   └── Dockerfile             # copied from brapper/deploy/
├── package.json               # bin: { "my-brap-mcp": "dist/mcp.js" }
└── tsconfig.json

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Getting started

pnpm add brapper puppeteer-core hono @hono/node-server

See docs/creating-a-brap.md for a step-by-step guide.

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Links

• Roadmap
• Contributing
• Architecture
• Creating a brap
• Concurrency model
• Session gate and monitor

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License

MIT © grigoreo-dev