Use the CLI from a coding agent

A coding agent that can run shell commands can use a gateway through faustine, with no MCP server to configure. The agent lists the operations, reads the inputs of the one it needs and calls it, the same three commands a person runs.

To connect an agent over MCP instead, see Connect clients.

Before you begin

The CLI is installed on the machine where the agent runs. See Install the CLI and sign in.
An API key for the gateway. Create one for the agent, with the scope it needs, so you can revoke it without affecting anyone else. See Create an API key.

Give the agent the gateway and the key

Set two environment variables in the shell the agent starts from. FAUSTINE_GATEWAY is the gateway's MCP URL and FAUSTINE_API_KEY is the key.

terminal

export FAUSTINE_GATEWAY=https://gateway.faustine.ai/<workspace>/<gateway>/mcp
export FAUSTINE_API_KEY=fik_…

With both set, faustine does not use the credentials file, so the agent works the same on your machine and in CI.

Tell the agent what to run

The agent needs three commands. Put them in its instructions, such as the CLAUDE.md or AGENTS.md of your repository:

Use the `faustine` command to work with Nimbus CRM.
- `faustine ops [query]` lists the operations.
- `faustine help <operation>` shows the inputs and an example.
- `faustine call <operation> --field value` runs it.
Run `faustine help <operation>` before the first call to an operation.

faustine --help prints the same sequence, so an agent that explores the command finds it without instructions.

Run it from Claude Code

Allow the faustine command and give the task. This example runs Claude Code once, without a session:

terminal

claude -p --allowedTools "Bash(faustine *)" "List the contacts added this week and create a follow-up deal for each one"

For Claude Code over MCP, see Connect Claude Code.

Give the agent the gateway's skill file

Each gateway publishes a skill file that describes the system behind it and how to discover its operations. faustine skill downloads it:

terminal

mkdir -p .claude/skills/nimbus-crm
faustine skill --out .claude/skills/nimbus-crm/SKILL.md

.claude/skills/<name>/SKILL.md is where Claude Code loads skills from a repository. For another agent, save the file where that agent reads its instructions.

What the agent gets back

Behavior	Detail
Output	JSON whenever the output is not a terminal, which is the case for an agent.
Errors	A JSON object on standard error: `{"error":{"code":"…","message":"…"}}`. `code` is stable.
Exit codes	`0` success, `1` wrong command, `2` credential, `3` refused by the gateway, `4` your API or the gateway failed, `5` network.
Prompts	None when the input is not a terminal.
Status lines	Informational lines go to standard error. `--quiet` removes them.

An unknown input field fails with exit code 1 and the list of valid fields, which the agent uses to correct the call.

The gateway applies the key's settings to every call. A read-only key gets read_only on a write, and an operation that requires confirmation gets requires_confirmation unless the key is allowed to run it. See Confirmation.

Next steps

Call an operation from the CLI: how inputs are passed and what each error means.
faustine CLI: every command, environment variable and exit code.
Connect Claude Code: use the gateway over MCP instead of the shell.