# Casper Devnet Launcher (Rust)
Casper Devnet Launcher is a Rust local development Casper network, based on and heavily inspired
by the NCTL workflow, to make local devnets quick and easy for smart contract developers.
It embeds the essential node-launcher behavior in-process, so you only need the `casper-node`
and (optionally) `casper-sidecar` binaries.
## Why this exists
NCTL is fantastic for core protocol development and for building assets from source trees, but it
comes with a large shell script surface, external process supervision, and multi-step UX. This tool
targets application and contract developers who want a repeatable, portable devnet for development,
CI, and tests.
## Comparison with NCTL
| Primary audience | Core protocol development | Smart contract/app developers, CI/tests |
| Process control | External supervisor (supervisord) | In-process process control |
| Setup workflow | Multiple commands | Single command: `casper-devnet start` |
| Implementation | Large shell script | Rust binary (portable) |
| Node launcher | External `casper-node-launcher` | Embedded launcher logic |
| Requirements | Node + launcher + sidecar + scripts | Assets bundle (node + sidecar + templates) |
| Keys/accounts | Random keys, friction to name/locate | Deterministic keys from a seed (BIP32 paths) |
| macOS devnet start | Often requires extra local compilation | Planned: download pre-built bundles |
| Network feedback | Extra commands to watch blocks/txs | Persistent SSE connection with live output |
## Requirements
- A local assets bundle (`.tar.gz`) containing binaries and templates (see below)
## Usage
Add a local assets bundle:
```bash
casper-devnet assets add /path/to/assets-bundle.tar.gz
```
Download assets from the latest release:
```bash
casper-devnet assets pull
```
Force re-download:
```bash
casper-devnet assets pull --force
```
Override the target triple:
```bash
casper-devnet assets pull --target x86_64-unknown-linux-gnu
```
## Security note
`casper-devnet assets pull` downloads pre-built binaries from
`https://github.com/veles-labs/devnet-launcher-assets/releases`.
If you are not comfortable running pre-built binaries, download the assets repo and rebuild the
binaries locally using the provided scripts before installing them with `assets add`.
List available protocol versions:
```bash
casper-devnet assets list
```
Start a devnet:
```bash
casper-devnet start
```
Create assets without starting processes:
```bash
casper-devnet start --setup-only
```
Use `--setup-only` when you want to tweak chainspecs or node configs before launching.
Rebuild assets:
```bash
casper-devnet start --force-setup
```
## Common flags
- `--protocol-version <version>`: Protocol version to use from the assets store (defaults to newest bundle)
- `--network-name <name>`: Network name for configs/paths (default: `casper-dev`)
- `--node-count <n>`: Number of nodes (aliases: `--nodes`, `--validators`; default: 4)
- `--users <n>`: Number of user accounts (default: node count)
- `--delay <seconds>`: Genesis activation delay (default: 30)
- `--loglevel <level>`: Child process log level (default: `info`)
- `--node-log-format <format>`: Node logging format in config (default: `json`)
- `--setup-only`: Build assets and exit
- `--force-setup`: Rebuild assets even if they exist
- `--seed <string>`: Seed for deterministic devnet keys (default: `default`)
## Assets bundle layout
The bundle is extracted into the platform data directory and should include a versioned root with
the following shape:
```
v2.1.1/bin/casper-node
v2.1.1/bin/casper-sidecar
v2.1.1/chainspec.toml
v2.1.1/sidecar-config.toml
v2.1.1/node-config.toml
```
For manual rebuilds and bundle scripts, see
`https://github.com/veles-labs/devnet-launcher-assets/`.
## Notes
- The launcher runs the node directly and manages processes internally; no external supervisor is required.
- The embedded launcher state is handled within the process; only the node/sidecar binaries are required.
- Assets are stored under the platform data directory (e.g., `~/.local/share/xyz.veleslabs.casper-devnet` on Linux or `~/Library/Application Support/xyz.veleslabs.casper-devnet` on macOS), with `assets/` for bundles and `networks/` for runtime assets.