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Arbiter CLI Reference

arbiter is the client-facing command for agents and humans. It talks to an Agent Arbiter MCP server and exposes capability, account, operation, and raw MCP commands.

Most users should start with cap, accounts, and op. The raw mcp commands are available for inspection and debugging.

Agent Arbiter keeps MCP tool count small by exposing a hierarchical discovery surface. Start broad with capabilities, then drill into accounts and operation schemas before running an operation:

arbiter cap
arbiter cap desc smtp
arbiter accounts desc smtp bot
arbiter op desc smtp:send_email

Global options​

arbiter [--config-dir DIR] [--config-name NAME] <command>
  • --config-dir DIR: client config directory. Defaults to ~/.arbiter.
  • --config-name NAME: client config file name without .yaml. Defaults to arbiter-client.
  • --version: print the installed version.

The client reads mcp_url from its config. You can override it per command with a Hydra-style argument:

arbiter cap mcp_url=http://127.0.0.1:8000/mcp

Default client config:

~/.arbiter/arbiter-client.yaml

Example:

mcp_url: http://127.0.0.1:8000/mcp

bootstrap​

Create the client config file.

arbiter bootstrap client [--force] [override...]
  • --force: overwrite an existing client config.

Example:

arbiter bootstrap client mcp_url=http://127.0.0.1:8000/mcp

Common flow​

arbiter cap
arbiter cap desc smtp
arbiter accounts
arbiter accounts desc smtp bot
arbiter op desc smtp:send_email
arbiter op run smtp:send_email --args '{"account":"bot","to":["ops@example.com"],"subject":"Hello","text_body":"Hi"}'

cap​

Discover capability names and descriptions.

arbiter cap [list] [--json]
arbiter cap desc [capability]
  • cap and cap list: list capability names.
  • cap list --json: print capability names as JSON.
  • cap desc: describe all capabilities with bounded summaries.
  • cap desc <capability>: describe one capability.
  • capabilities is an alias for cap.
  • describe is an alias for desc.

Bounded summaries include capability descriptions, account counts, operation counts, and limited previews. Operators configure preview limits under arbiter.discovery.

accounts​

Inspect configured accounts exposed through capabilities.

arbiter accounts [list] [--json]
arbiter accounts desc <capability> [account]
  • accounts and accounts list: list accounts grouped by capability.
  • accounts list --json: print account names as JSON.
  • accounts desc <capability>: describe accounts for one capability.
  • accounts desc <capability> <account>: describe one account.
  • describe is an alias for desc.

op​

Inspect and run operations.

arbiter op desc <operation-id>
arbiter op run <operation-id> --args '<json-object>'
  • op desc: describe one operation, such as smtp:send_email.
  • op run: run one operation with JSON arguments.
  • operation is an alias for op.
  • describe is an alias for desc.

Example:

arbiter op run smtp:send_email --args '{"account":"bot","to":["ops@example.com"],"subject":"Hello","text_body":"Hi"}'

mcp​

Inspect and call raw MCP tools.

arbiter mcp [tools] [--json]
arbiter mcp call <tool-name> --args '<json-object>'
  • mcp and mcp tools: list raw MCP tools.
  • mcp tools --json: print full tool metadata as JSON.
  • mcp call: call a raw MCP tool by name.