> ## Documentation Index > Fetch the complete documentation index at: https://docs.boat.dev/llms.txt > Use this file to discover all available pages before exploring further. # Customize the harness > Add house rules, MCP servers, skills and tools to the harnesses on a sandbox, reach your own app, or bring your own harness. Every harness reads its own config files from the sandbox home. Boat adds only two things: * A short system prompt. It tells the harness that it runs headless in a sandbox, and that the `boat` CLI exists. * The `boat` skill. You add everything else. Use any of these: * `boat ssh`, `boat exec` or `boat scp` * a file that the agent writes * an [environment setup script](/environments) * a [named snapshot](/snapshots), so every new sandbox starts with it We tested each row on this page end to end through `boat prompt`, on the current harness versions. Each row names the file that changed the answer of the harness. ## Instructions and hidden rules Add a rules file. Every prompt on that sandbox then obeys it, even when the prompt does not mention it: | Harness | Files read (all applied together) | Not read | | - | - | - | | Claude Code | `~/CLAUDE.md`, `~/.claude/CLAUDE.md` | `AGENTS.md` | | Codex | `~/AGENTS.md`, `~/.codex/AGENTS.md` | `config.toml` `developer_instructions` (Boat sets the base instructions) | | pi | `~/AGENTS.md`, `~/.pi/agent/AGENTS.md`, `~/.pi/agent/APPEND_SYSTEM.md` | `CLAUDE.md` when an `AGENTS.md` exists | | OpenCode | `~/AGENTS.md`, `~/.config/opencode/AGENTS.md`, files listed in `opencode.json` `instructions` | | | Prime Agent | `~/AGENTS.md`, `~/.prime/agent/AGENTS.md`, `~/.prime/agent/APPEND_SYSTEM.md` | | | Kimi Code | `~/AGENTS.md`, `~/.kimi-code/AGENTS.md`, `~/.agents/AGENTS.md` | `CLAUDE.md` | | Mistral Vibe | `AGENTS.md` at the root of a git repository it works in, after you trust that folder (`~/.vibe/trusted_folders.toml`) | `~/AGENTS.md`, `CLAUDE.md`. Use a skill for house rules | * One `~/AGENTS.md` plus one `~/CLAUDE.md` covers every harness except Mistral Vibe. * `APPEND_SYSTEM.md` (pi, Prime) goes at the end of the system prompt itself, not into the project context. * When an environment clones a single repository, Claude Code starts inside that repository. So a `CLAUDE.md` there also applies. ```bash theme={null} boat exec "printf '# House rules\nAlways run the test suite before saying you are done.\n' > ~/AGENTS.md; cp ~/AGENTS.md ~/CLAUDE.md" ``` ## MCP servers | Harness | How to register | Config written | | - | - | - | | Claude Code | `claude mcp add --scope user -- ` | `~/.claude.json` (project scope: `~/.mcp.json`) | | Codex | `codex mcp add -- ` | `~/.codex/config.toml` `[mcp_servers.]` | | pi | `pi install npm:pi-mcp-extension`, then `~/.pi/agent/mcp.json` | `{"mcpServers": {"": {"transport": "stdio", "command": …, "lifecycle": "eager"}}}` | | OpenCode | `~/.config/opencode/opencode.json` | `"mcp": {"": {"type": "local", "command": [...]}}` | | Prime Agent | `prime-agent mcp add -- ` | `~/.prime/agent/settings.json` `mcpServers` | | Kimi Code | `~/.kimi-code/mcp.json` | `{"mcpServers": {"": {"command": …, "args": [...]}}}` (`{"url": …}` for HTTP) | | Mistral Vibe | `~/.vibe/config.toml` | `[[mcp_servers]]` with `name`, `transport = "stdio"`, `command`, `args` (`url` for HTTP) | * Remote (HTTP) servers work the same way, with a URL instead of a command. * On a sandbox, the MCP resource browsing tools of Claude Code are turned off. MCP tools stay on. Every sandbox already has one server registered this way: `computer`, in these same files. Your server next to it does not change it, and it never overwrites yours. Read [Computer use](/integrated-agents/computer-use). ## Reach your own app from the sandbox A sandbox has no route back to your laptop. So the agents in it cannot see an MCP server, a local model, or a webhook receiver on your `localhost`. `boat forward --reverse` opens that route. A port on your machine then answers at `127.0.0.1:` inside the sandbox. It uses the same SSH session as `boat ssh`. Nothing is public on either end. ```bash theme={null} # leave this running; your MCP server on localhost:7777 is now in the sandbox boat forward bx_f7k2q9hd --reverse --local 7777 ``` Register it one time inside the sandbox. Then every harness can call it: ```bash theme={null} boat exec bx_f7k2q9hd "claude mcp add --scope user mine --transport http http://127.0.0.1:7777/mcp" ``` * The registration is in the sandbox home. It survives `boat stop`, `boat resume`, and `boat fork`. * The tunnel does not survive. Start it again the next time the agent must reach you. * A local model works the same way. `boat forward --reverse --local 11434` puts Ollama on `http://127.0.0.1:11434` inside the sandbox. Any harness that uses that base URL can call it. For the flags and the redial behaviour, read [`boat forward --reverse`](/cli-reference#--reverse-reach-your-machine-from-the-sandbox). Products that do not ship the CLI can open the same tunnel. The CLI only wraps stock OpenSSH: ```bash theme={null} # 1. authorize your public key on the sandbox; the reply carries machineIp curl -s -X POST https://boat.dev/api/v1/sandboxes/$BOAT_ID/sshkey \ -H "Authorization: Bearer $BOAT_API_KEY" -H 'Content-Type: application/json' \ -d "{\"key\": \"$(cat ~/.ssh/id_ed25519.pub)\"}" # 2. open the reverse tunnel and leave it running ssh -o ExitOnForwardFailure=yes -i ~/.ssh/id_ed25519 -N -R 7777:127.0.0.1:7777 user@ ``` ## Skills A skill is a folder with a `SKILL.md` file. The file has frontmatter with `name` and `description`, then the instructions. Every harness on a sandbox already has a skills directory with the `boat` skill in it. Add yours next to it: | Harness | Skills directory | | - | - | | Claude Code | `~/.claude/skills//SKILL.md` | | Codex | `~/.codex/skills//SKILL.md` | | pi | `~/.pi/agent/skills//SKILL.md` | | OpenCode | `~/.config/opencode/skills//SKILL.md` | | Prime Agent | `~/.prime/agent/skills//SKILL.md` | | Kimi Code | `~/.kimi-code/skills//SKILL.md` (also `~/.agents/skills//SKILL.md`) | | Mistral Vibe | `~/.vibe/skills//SKILL.md` (also `~/.agents/skills//SKILL.md`) | ## Command-line tools Anything on `PATH` is a tool. To add one, do one of these: * Put a script in `~/.local/bin` or `/usr/local/bin`. * Install it with `npm i -g`, `pip install` or `apt install`. Then ask for it by name. All seven harnesses run it through their shell tool. ## Custom in-process tools and extensions Use these when a tool must show as a native function call, not a shell command: | Harness | Mechanism | Path | | - | - | - | | pi | extension calling `pi.registerTool({...})` | `~/.pi/agent/extensions/.ts` | | Prime Agent | same extension API | `~/.prime/agent/extensions/.ts` | | OpenCode | `tool({description, args, execute})` from `@opencode-ai/plugin` (dependencies install themselves on first run) | `~/.config/opencode/tools/.ts` | | Claude Code | hooks in `~/.claude/settings.json`, plugins | see [Claude Code docs](https://code.claude.com/docs/en/hooks) | | Codex | hooks in `~/.codex/hooks.json` | see [Codex docs](https://learn.chatgpt.com/docs/hooks) | | Kimi Code | `[[hooks]]` in `~/.kimi-code/config.toml`, plugins | see [Kimi Code docs](https://www.kimi.com/code/docs/en/kimi-code-cli/customization/hooks.html) | | Mistral Vibe | hooks in `~/.vibe/hooks.toml` | see [Mistral Vibe on GitHub](https://github.com/mistralai/mistral-vibe#hooks) | ## What is shared, what persists * **Config is per sandbox, not per conversation.** Every parallel conversation on a sandbox reads the same home directory, whatever its harness. There is one `AGENTS.md`, one skills folder, one MCP list. For rules per user, use a sandbox per user, or put the rules in the prompt. * **Boat captures everything in `/home/user` on stop.** Rules, MCP registrations, skills, extensions, tools you installed under home, and the harness sessions all come back on `boat resume` and `boat fork`. Tools installed outside home (`apt`, `/usr/local`) are also part of the system snapshot. * **Set it up one time.** An [environment](/environments) setup script or a [named snapshot](/snapshots) gives every new sandbox the same rules, tools and servers from the first prompt. ## Bring your own harness The built-in harnesses are ordinary binaries on `PATH`. They have the same credentials that the agent server uses. You have three ways to go further than `boat prompt`: * **Run a built-in harness yourself.** Use `boat ssh` or `boat exec`. Run `claude`, `codex`, `pi`, `opencode`, `prime-agent`, `kimi`, or `vibe` (Mistral Vibe) directly, in any mode they support. The agent server does not lock the files or the processes. * **Install a harness that Boat does not ship.** Run `boat exec "npm i -g "`, or add it to an environment or a snapshot. Run it over `boat exec` or SSH. It works next to the built-in harnesses and reads the same per-sandbox `-e` keys. * **Run your own agent loop.** Put a small HTTP daemon in the sandbox and talk to it directly. The [Platform Guide](/platform-guide/agents#bring-your-own-harness-the-daemon-pattern) shows how. `boat host` gives it a URL. [Webhooks](/webhooks) tell your control plane when the sandbox is up. Whatever you run, these keep working: `boat events`, attachments under `~/attachments`, [desktop streaming](/desktop-streaming), snapshots, and forks. This documentation is built and hosted on [Mintlify](https://mintlify.com), a developer documentation platform.