Getting Started

Local install

Run arbiter on your own machine. You bring the provider keys; you control the binary. Free, open-source, fully featured. Ten minutes from curl to first agent reply.

If you'd rather call arbiter without operating it, see the hosted preview instead.

Prerequisites

  • A provider key for whichever model family you want agents to use:
    • Anthropic — ANTHROPIC_API_KEY (or save to ~/.arbiter/api_key).
    • OpenAI — OPENAI_API_KEY (or save to ~/.arbiter/openai_api_key).
    • Google Gemini — GEMINI_API_KEY (or save to ~/.arbiter/gemini_api_key).
    • Ollama — set OLLAMA_HOST if not at http://localhost:11434.
  • Only one is required. Multiple can coexist; different agents can target different providers.
  • Optional: a Brave Search key (ARBITER_SEARCH_API_KEY) if you want /search to resolve. Without it, agents fall back to /fetch on URLs they already know.

Install the binary

macOS arm64

curl -L https://github.com/tylerreckart/arbiter/releases/latest/download/arbiter-macos-arm64.tar.gz \
  | tar xz -C /usr/local/bin

Linux x86_64

curl -L https://github.com/tylerreckart/arbiter/releases/latest/download/arbiter-linux-x86_64.tar.gz \
  | tar xz -C /usr/local/bin

From source (any platform with C++20)

git clone https://github.com/tylerreckart/arbiter.git
cd arbiter
cmake -B build -DCMAKE_BUILD_TYPE=Release
cmake --build build
sudo cmake --install build

Build deps: OpenSSL, libcurl, SQLite3, a C++20 compiler. libedit or GNU readline is optional but recommended for line editing in the terminal client. Distro-specific install commands are in CONTRIBUTING.md.

First run

export ANTHROPIC_API_KEY="sk-ant-..."   # or OPENAI_API_KEY / GEMINI_API_KEY
arbiter --init                          # seed ~/.arbiter/ with starter agents
arbiter                                 # launch the terminal client

--init writes nine starter agents into ~/.arbiter/agents/*.json (reviewer, research, writer, devops, planner, backend, frontend, marketer, social) and is safe to re-run — existing files are preserved unless you pass --force. See cli/init.md for the full layout.

arbiter opens the interactive TUI. Type a message and the master agent (index) decides whether to answer directly or delegate. Switch agents with /use <name>; send a one-off to a specific agent with /send <name> <message>. Full TUI reference: tui/.

Try one-shot mode

For scripts and CI hooks:

arbiter --send reviewer "review: if (arr.length = 0) return;"

The agent runs the full orchestration loop internally — tool calls, sub-agent delegation, advisor gating — and prints the final reply on stdout. See cli/send.md.

Run as an HTTP server

If you want other clients (web UIs, automations, mobile) to drive arbiter:

arbiter --add-tenant me                       # prints the bearer token — save it
arbiter --api --port 8080                     # bind 127.0.0.1 by default

Authenticate with Authorization: Bearer <token>. The endpoint catalogue is at api/. Production deployments belong behind a reverse proxy for TLS and rate limiting — see concepts/operations.md.

Where things live

~/.arbiter/
├── agents/*.json          agent constitutions (edit these)
├── api_key                Anthropic key (alternative to env var)
├── openai_api_key         OpenAI key
├── gemini_api_key         Google Gemini key
├── tenants.db             tenant identities for --api
├── sessions/              per-cwd TUI session snapshots
├── memory/                per-agent persistent scratchpads
├── mcp_servers.json       optional MCP server registry
└── a2a_agents.json        optional remote A2A agent registry

Full reference: cli/environment.md.

Next steps