LangBot ships four extension mechanisms in parallel — plugins, MCP, Skills, and the sandbox — and they are easy to confuse. This page sorts out what each one does and when to use it.
One-line Summary
- Sandbox: an execution environment that lets the Agent run commands and read/write files
- Skills: on-demand instruction packages that hand the Agent a specialized workflow when needed
- MCP Server: connects to external tool services
- Plugin: a long-running extension process that can ship its own config page, event listeners, and knowledge components
Comparison
| Capability | Provided by | How the Agent sees it | When to use |
|---|
| Sandbox | Box Runtime | The six tools exec/read/write/edit/glob/grep are attached directly | Agent needs to run code or read/write files |
| Skills | Box Runtime skill store | After the Agent calls activate, instructions are injected via Tool Result | Hand the Agent a workflow, template, or script, triggered on demand |
| MCP Server | LangBot MCP Loader (stdio mode is hosted by Box) | Tools land directly in the Agent’s tool list | Connect an existing MCP service |
| Plugin | Plugin Runtime | Capabilities are exposed through the plugin system | Long-lived capability with a config page, event listeners, or knowledge components |
Pipeline Binding
Skills, MCP Servers, and plugins are all pipeline extensions. After installing or creating them in the WebUI, the pipeline extension config still decides where they’re enabled:
- Enable all extensions, or
- Bind only specific extensions
Skill binding decides which skills the Agent can see (it controls the <available_skills> list). The actual skill content is only injected after the Agent calls activate.
Troubleshooting Map
| Symptom | Check first |
|---|
Agent has no exec/read/write tools | box.enabled, backend availability, and whether the pipeline uses the built-in Agent |
| Skill list is empty | Box Runtime status, box.local.skills_root, pipeline binding |
| stdio MCP fails to start | Box Runtime status, MCP command and environment variables, startup timeout |
| Sandbox fails to start in Docker deployment | Whether langbot_box mounts docker.sock, and whether Box root paths match |
| File read/write fails | box.local.host_root, box.local.allowed_mount_roots |
| Backend selection has no effect | Confirm BOX__BACKEND is set on the langbot service, not on langbot_box |
Sandbox built-in tools and Skills currently target the built-in Agent. External runners (Dify, n8n, Langflow, Coze, etc.) should use their own tools and execution model.
