# What is the Model Context Protocol (MCP)?

The Model Context Protocol (MCP) is an open standard for connecting AI applications to external tools, data sources and workflows.

**Runtime's MCP server gives an agent every Runtime product as tools, and it
connects with one browser approval and no key to copy.** Claude Code, Codex,
Cursor, ChatGPT, VS Code and any client that speaks MCP can create sandboxes,
run code, read files and fork machines through it ([MCP](/docs/mcp)).

## Why it matters for AI agents

Before MCP, each AI application needed its own integration for each tool it
used. MCP gives both sides one protocol: a tool is written once as an MCP
server, and every MCP client can use it. The project's own description compares
it to "a USB-C port for AI applications". Anthropic open-sourced it on
25 November 2024, and it is now supported by Claude, ChatGPT, Visual Studio
Code, Cursor and many other clients.

## MCP in facts

| Fact            | Value                                                                         |
| --------------- | ----------------------------------------------------------------------------- |
| What it is      | An open protocol between LLM applications and external data and tools         |
| Message format  | JSON-RPC 2.0, UTF-8 encoded                                                   |
| Roles           | Hosts (LLM applications), clients (connectors inside a host), servers         |
| Server features | Resources (context and data), prompts (templated messages), tools (functions) |
| Client features | Elicitation: a server asks the user for more information                      |
| Transports      | stdio, to a client-launched subprocess; Streamable HTTP, to one endpoint      |
| Latest revision | 2026-07-28                                                                    |

Source: the MCP specification at modelcontextprotocol.io, read on
25 September 2026. The specification treats tools as arbitrary code execution
and requires hosts to obtain the user's consent before invoking one.

## Runtime's MCP server

Add it to Claude Code or Codex with one command:

```bash no-run
claude mcp add --scope user runtime -- npx -y withruntime mcp
codex mcp add runtime -- npx -y withruntime mcp
```

The first time, the server offers one tool, `runtime_connect`. The agent calls
it and shows you a link and a code, you approve **Connect agent** in your
browser, and every Runtime tool appears with nothing to restart. The command is
a bridge: it forwards MCP messages to the remote server over the saved
connection, so no key sits in the agent's configuration.

Clients that speak MCP over HTTP connect directly to
`https://api.withruntime.com/mcp` over Streamable HTTP and sign in through the
browser with OAuth 2.1 and PKCE ([remote connection](/docs/mcp#remote-connection)).

| Tool                              | What it does                                                        |
| --------------------------------- | ------------------------------------------------------------------- |
| `runtime_sandbox_create`          | Create a sandbox and wait until it is ready                         |
| `runtime_sandbox_exec`            | Run a command and get its exit code and output                      |
| `runtime_sandbox_files_write`     | Write a file into the sandbox                                       |
| `runtime_sandbox_interpreter_run` | A notebook-style session in Python, JavaScript, TypeScript and more |
| `runtime_sandbox_fork`            | Copies of a sandbox as it is now, with its memory and processes     |
| `runtime_sandbox_network_set`     | Replace a sandbox's network rules                                   |
| `runtime_limits_get`              | Whether this key is read-only, and its daily spending limit         |

Tool names read `runtime_<product>_<verb>`. The server sends instructions on
first contact: the quick start, safe retries and how to report problems. The
full list is in [tools](/docs/mcp#tools).

A sandbox can also run MCP servers of its own, such as GitHub, Postgres or a
Playwright browser, at URLs your agent connects to
([MCP servers in a sandbox](/docs/javascript#mcp-servers-in-a-sandbox)).

## Related

- [Claude Code](/integrations/claude-code)
- [Codex](/integrations/codex)
- [What is an agent sandbox?](/glossary/agent-sandbox)
- [What is a code interpreter?](/glossary/code-interpreter)

## Sources

Checked 25 September 2026.

- [What is the Model Context Protocol?](https://modelcontextprotocol.io/docs/getting-started/intro)
- [MCP specification](https://modelcontextprotocol.io/specification/latest)
- [MCP transports](https://modelcontextprotocol.io/specification/2026-07-28/basic/transports)
- [Anthropic, Introducing the Model Context Protocol](https://www.anthropic.com/news/model-context-protocol), 25 November 2024

Facts on this page were checked on 25 September 2026.