> ## Documentation Index
> Fetch the complete documentation index at: https://docs.usefused.com/llms.txt
> Use this file to discover all available pages before exploring further.
# Harnest by Fused
> Fused's lightweight, compiled agent harness for going from zero to a complete, testable agent in minutes.
Harnest is a lightweight agent harness from [Fused](https://usefused.com) that takes agent building from zero to a complete, testable agent in minutes.
It manages the work around your agent while keeping the agent itself yours.
| Harnest manages | What you get |
| -------------------------------------- | ------------------------------------------ |
| Project structure and dependencies | A repeatable environment |
| Capability discovery and compilation | Only the capabilities you add |
| Tests and framework adapters | One workflow from source to verified agent |
| Serving, sessions, and approvals | A usable runtime without custom plumbing |
| Authentication, storage, and telemetry | Production-shaped boundaries |
| Development playground | A testable UI in seconds |
Every Harnest agent is compiled from the capabilities you add. Tools, subagents, MCP connections, agent skills, plugins, sandboxes, and lifecycle extensions are left out unless you use them.
## Managed and advanced modes
| Mode | Harnest manages | You control |
| -------- | ------------------------------------------------------------------ | --------------------------------- |
| Managed | Discovery, wiring, framework adapters, tests, and runtime services | Portable agent behavior |
| Advanced | Packaging, tests, serving, sessions, auth, and telemetry | The underlying framework directly |
Harnest builds on the work of [Google ADK](https://google.github.io/adk-docs/) and [LangGraph](https://docs.langchain.com/oss/python/langgraph/overview). Managed mode gives you the fastest path. Advanced mode lets you break out to native framework APIs without giving up the harness around them.
Existing agents can start in advanced mode and move compatible capabilities into the managed structure over time. See [Migrate a project](/harnest/get-started/migrate).
## Install
```bash theme={null}
curl -fsSL \
https://raw.githubusercontent.com/Usefused/harnest/main/install.sh |
sh
```
```bash theme={null}
harnest --version
harnest doctor
```
[Installation and releases](/harnest/reference/installation-and-releases) covers version pinning, CI installation, upgrades, checksums, and private forks.
## Initialize a project
Choose a framework:
```bash ADK theme={null}
harnest init support-agent --framework adk
```
```bash LangGraph theme={null}
harnest init support-agent --framework langgraph
```
Then sync and test the isolated environment:
```bash theme={null}
harnest env sync support-agent
harnest test support-agent
```
| Option | Result |
| ----------- | ------------------------------------------------------------------------- |
| Default | Small, runnable managed agent |
| `--example` | Adds working tools, graphs, plugins, skills, extensions, evals, and tests |
`compile`, `test`, and `serve` sync automatically. Add only your packages to `pyproject.toml`; Harnest owns the framework dependency.
## Migrate a project
### Bring an existing agent into Harnest
| Existing agent | Best starting point |
| --------------------------------------------------------------- | ------------------- |
| Uses portable agents, tools, and graphs | Managed mode |
| Depends on native plugins, middleware, state, or framework APIs | Advanced mode |
Start with the mode that preserves your current behavior. Harnest adds tests, serving, sessions, auth, storage, telemetry, and the playground around it. Move native pieces into managed capabilities only when that improves the project.
### Upgrade an older Harnest project
Preview first, then apply and test:
```bash theme={null}
harnest upgrade existing-agent
harnest upgrade existing-agent --apply
harnest test existing-agent
```
The first command previews the change. Apply verifies the reviewed files and creates backups.
### Switch between ADK and LangGraph
For a managed agent, change `spec.framework.name` in `config.yaml`:
```yaml theme={null}
spec:
framework:
name: langgraph # or adk
mode: managed
```
Test and serve the target framework:
```bash theme={null}
harnest test existing-agent
harnest serve existing-agent
```
Review native extensions, evals, sandboxes, custom nodes, and active checkpoints first. Advanced projects need a manual migration.
Follow the full [framework migration checklist](/harnest/runtime/adk-and-langgraph#switch-frameworks).
## Serve a project
```bash theme={null}
harnest serve support-agent
```
| URL | Use it for |
| ------------------------------- | -------------------------------- |
| `http://127.0.0.1:8080/` | Test the agent in the playground |
| `http://127.0.0.1:8080/docs` | Inspect the generated API |
| `http://127.0.0.1:8080/healthz` | Check process health |
The playground and neutral API work in both modes. Configure runtime properties in `server.yaml`.
## Explore Harnest
Learn the project concepts and where each capability belongs.
See what moves between ADK and LangGraph.
Add resources, storage, auth, hooks, and telemetry.
Use the neutral API, events, approvals, and playground.