# String > Markdown that runs — one file, any agent. - **Type:** MCP server - **Install:** `agentstack add mcp-string-os-string` - **Verified:** Yes — security-reviewed for prompt injection and unsafe behavior - **Seller:** [string-os](https://agentstack.voostack.com/s/string-os) - **Installs:** 0 - **Category:** [AI & ML](https://agentstack.voostack.com/c/ai-and-ml) - **Latest version:** 0.1.0 - **License:** MIT - **Upstream author:** [string-os](https://github.com/string-os) - **Source:** https://github.com/string-os/string - **Website:** https://string-os.org ## Install ```sh agentstack add mcp-string-os-string ``` Requires the [AgentStack CLI](https://agentstack.voostack.com/docs/cli). Works with Claude Code, Cursor, and any MCP-compatible agent. ## About # String **An app framework and browser for AI agents.** String unifies apps, the web, and Markdown documents into one agent-native surface. A website can expose navigation and actions in Markdown, so an agent can use it like an app. Ordinary web pages still open as clean Markdown. Installed apps, local documents, web pages, files, APIs, and shell sessions all use the same commands. The core loop is intentionally small: ```text /open read a document, app, web page, file, or shell session /act call an available action /info understand where you are ``` String can run as a CLI, a daemon, or one MCP tool named `string`. The agent learns one surface and uses it everywhere. Available String apps are maintained at [github.com/string-os/apps](https://github.com/string-os/apps). --- ## Why Most agent integrations grow the agent's context: another tool schema, another API manual, another set of examples. String moves that knowledge into the app or page itself. An agent opens a page, sees what actions are available, calls one, and follows the next hint. The page may be a local Markdown file, an installed app, an agent-native website, or a normal website rendered as Markdown. The interaction is the same. What changes: - **Apps and web share one model.** A String app and an agent-native web page expose the same surface: Markdown content, navigation, actions, state, and hints. - **One browser for agent work.** `/open`, `/act`, `/info`, and topics work the same for documents, apps, web pages, files, APIs, and shell sessions. - **Self-discovery.** Actions expose schemas with `/act --help`; responses carry `next:` hints; errors carry recovery hints. - **Local command boundary.** Web-hosted SFMD can call web APIs, but local shell commands run only from local files or locally installed apps. - **Agent event inbox.** Local webhooks can deliver text events to an agent, which reads and acknowledges them through the same CLI/MCP surface, or receives as a Claude Code channel notification. - **Credentials stay scoped.** App secrets are set inside app topics with `/set $VAR = "..."`, not pasted into the agent's prompt. - **Portable by default.** A String surface is Markdown. It can live in a file, an installed package, a GitHub repo, or on the web. String calls this format **SFMD**: String Flavored Markdown. It is normal Markdown plus lightweight navigation, action blocks, and response conventions. --- ## One Surface No SDK. No endpoint memorized. The surface tells the agent what it can do. Open a web page as Markdown: ```bash string main '/open https://docs.string-os.org/runtime/mcp' ``` Open an installed app and follow its actions: ```bash string app:moltbook '/open' # [actions] home, feed, read, comment, post, search # next: /act.feed · /act.search "..." string app:moltbook '/act.feed' # Feed: @post-1 through @post-20 # next: /act.read @post-N string app:moltbook '/act.read @post-3' # ...post body... # next: /act.comment @post "..." ``` The same interaction over MCP is one tool call: ```json { "topic": "app:moltbook", "cmd": "/act.read @post-3" } ``` --- ## Install ### Claude Code Plugin ```text /plugin marketplace add string-os/string /plugin install string@string-os ``` This installs the String MCP tool and a short skill for using it. The tool is registered as server `string` and exposes one tool named `string`. For multiple local agents or workspace-specific homes, see [Agent Identity](./docs/start/agent-identity.md). To receive local String webhook events directly inside Claude Code, launch Claude Code with the String plugin channel and select the local agent id: ```bash string agent add leo --home /home/ubuntu/crew/leo STRING_AGENT_ID=leo \ claude \ --dangerously-load-development-channels plugin:string@string-os ``` That keeps the plugin-provided `string` MCP tool available and also pushes local events for the selected String agent into the Claude Code session. The official Discord channel can be loaded at the same time with `--channels plugin:discord@claude-plugins-official`. ### Codex Plugin ```bash codex plugin marketplace add string-os/string codex plugin add string@string-os ``` ### CLI ```bash npm install -g @string-os/string string --help ``` The daemon starts automatically on first use. Default port: `3923`. --- ## Basic CLI ```bash string main '/open ./README.md' string main '/open https://docs.string-os.org/runtime/mcp' string app:weather '/act.now Seoul' string bash:dev 'pwd && ls' ``` Topics scope state: | Topic | Use | |---|---| | `main`, `notes`, `research` | free-form document/web sessions | | `app:` | installed app session | | `app::` | app session with config-scoped env | | `bash:` | persistent shell session | | `app`, `tool`, `bash`, `event`, `system`, `agent` | hub topics for runtime views and management | Hub topics are reserved. Open them to inspect runtime state, or send management commands through their hub: ```bash string app # installed apps + active app sessions string event # event inbox + local webhook URL string system status string agent list ``` Every response is wrapped so an agent can separate String output from shell noise: ```text ... ``` --- ## MCP String serves MCP directly. No separate MCP package is needed. ```json { "mcpServers": { "string": { "command": "npx", "args": ["-y", "@string-os/string", "--mcp"] } } } ``` The MCP tool takes: ```json { "topic": "main", "cmd": "/info" } ``` For local webhook event delivery into Claude Code Remote Control channels, see [Events and Local Webhooks](./docs/runtime/events.md). Use `/help`, `/info`, and `/act --help` to discover what is available. --- ## Surfaces, Not SDKs A String surface can be: - a local Markdown document - an installed app - a web page that exposes Markdown navigation and actions - an ordinary web page rendered as Markdown - a shell session or file workspace The agent uses the same commands either way. When a surface includes SFMD action blocks, it becomes executable. ````markdown --- name: weather type: app default: now --- # Weather ```act.now GET https://wttr.in/{city}?format=%l:+%C+%t+%w&m city, -c: string (required) "City name" ``` ```` Install that file as an app and call it: ```bash string main '/install --app ./weather.md' string app:weather '/act.now Seoul' ``` The Markdown is the interface. The runtime handles discovery, argument parsing, execution, output framing, state, and credentials. --- ## Docs - [Documentation](https://docs.string-os.org) - [Agent Identity](./docs/start/agent-identity.md) - [MCP](./docs/runtime/mcp.md) - [Runtime Overview](./docs/runtime/overview.md) - [SFMD Overview](./docs/sfmd/overview.md) - [Cookbook](https://github.com/string-os/cookbook) ## Build an SFMD site Want a website that serves styled HTML to people and a clean `.md` twin to agents? - [`site-builder`](https://github.com/string-os/site-builder) — a Claude Code / Codex plugin that scaffolds, validates, and deploys human + AI sites. Pure `npx`, no runtime dependency. - [`@string-os/astro-sfmd`](https://www.npmjs.com/package/@string-os/astro-sfmd) — the Astro integration it drives: every page emits HTML + a mirrored `.md`. ## Packages - `@string-os/string` — CLI, daemon, MCP server, runtime - `@string-os/client` — HTTP/SSE client for `stringd` - `@string-os/core` — SFMD parser - `@string-os/compiler` — SFMD validator/compiler - `@string-os/astro-sfmd` — Astro integration for human + AI (SFMD) sites ## License MIT ## Source & license This open-source MCP server is cataloged on AgentStack and links to its original source — we do not rehost the code. - **Author:** [string-os](https://github.com/string-os) - **Source:** [string-os/string](https://github.com/string-os/string) - **License:** MIT - **Homepage:** https://string-os.org Install and usage instructions live in the source repository linked above. ## Pricing - **Free** — Free ## Security capabilities Automated source analysis of v0.1.0 — what this tool can access: - **Network access:** no - **Filesystem access:** no - **Shell / process execution:** no - **Environment & secrets:** no - **Dynamic code execution:** no *"Yes" means the capability is present in the source — more access means more to trust, not that it is unsafe.* ## Versions - **0.1.0** — security scan: passed — Imported from the upstream source. ## Links - Listing page: https://agentstack.voostack.com/l/mcp-string-os-string - Seller: https://agentstack.voostack.com/s/string-os - Browse the marketplace: https://agentstack.voostack.com/browse --- Listed on AgentStack — the marketplace for AI agent skills and MCP servers. Every listing is security-reviewed. Creators keep 70%.