Local Install

Install Arbiter locally, seed the starter agents, and open the terminal workspace. You control the binary and configuration; model requests go to the provider you configure.

Prerequisites

  • A provider key for whichever model family you want agents to use:
    • OpenRouter — OPENROUTER_API_KEY (or save to ~/.arbiter/openrouter_api_key) for hosted models.
    • Ollama — set model ids to ollama/<model> for local models.
    • Ollama — set OLLAMA_HOST if not at http://localhost:11434.
  • Only one is required. Multiple can coexist; different agents can target different providers.
  • Optional: run arbiter --setup-tools to enable /search (Brave key), /browse (Playwright MCP), and other MCP servers. Without search configured, agents fall back to /fetch on URLs they already know.

Install the binary

The installer supports macOS Apple silicon and Linux x86_64, selects the newest published release containing a compatible binary, and verifies its SHA-256 checksum:

curl -fsSL https://arbiter.run/install.sh | sh

Review the installer source before running it if you prefer. Set INSTALL_DIR to install somewhere other than /usr/local/bin; the script uses sudo only when the target directory is not writable.

Pin a specific release:

curl -fsSL https://arbiter.run/install.sh | ARBITER_VERSION=v0.10.0 sh

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. Distro-specific install commands are in CONTRIBUTING.md.

First run

export OPENROUTER_API_KEY="sk-or-..."
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 arbiter --init 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 this first:

Help me turn this project into a concrete plan. Ask what you need to know, then delegate research and review to separate agents.

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 arbiter --send.

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 Operational notes.

Where things live

~/.arbiter/
├── agents/*.json          agent constitutions (edit these)
├── openrouter_api_key     OpenRouter key (alternative to env var)
├── search_api_key         Brave Search key for /search (via --setup-tools)
├── tenants.db             tenants, conversations (TUI + API), scratchpads, memory, schedules
├── conversations/         legacy TUI JSON archive + layout.json mirror
├── sessions/              legacy per-cwd snapshots (imported once)
├── mcp_servers.json       optional MCP server registry (via --setup-tools)
└── a2a_agents.json        optional remote A2A agent registry

Full reference: Environment.

Next steps

  • Author your own agent. Drop a JSON into ~/.arbiter/agents/<id>.json. Schema: POST /v1/agents. Concepts: Writ, Advisor.
  • Read the design philosophy. Philosophy.
  • Wire up integrations. arbiter --setup-tools for search / browse / MCP, or edit the files by hand — MCP servers, A2A.