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Send a fax from Gemini CLI

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Gemini CLI can send and read faxes for you through the Fax for Agents extension. One command installs it. The extension runs the Fax for Agents tool server on your machine with your API key, and you describe the fax in plain words. Gemini prepares the page, gets a quote and sends it. By default it sends inside the limits your organization set, with no approval per fax. This guide was recorded in Sandbox mode, so nothing reached a real fax line.

Screenshots taken on .

Before you start

  • A Fax for Agents account and an API key. On the API keys page, choose New key and keep the environment on test. Tick "This key is for a connected app such as Gemini CLI". Sandbox keys begin with ffa_test_ and are free.
  • Gemini CLI 0.62 or newer with a Gemini API key in your shell as GEMINI_API_KEY. The default model in Gemini CLI 0.62 is not open to new API keys. Start it with a current model, for example gemini -m gemini-3.5-flash-lite.
  • The Connected apps switch in Settings is on by default. The default limits are $5.00 per fax and 20 faxes a day.
  • Optional: a GEMINI.md in your folder that names the fax tools. The one used here reads: "Use the faxforagents tools for anything about faxes. To send: prepare_fax with the text, quote_fax with the number, then send_approved_fax with the quote id. For delivery evidence use get_fax_status. For the inbox use list_inbox and read_inbound_fax."

1.Install the extension

Open a terminal in the folder you work in. Run gemini extensions install https://github.com/faxforagents/gemini-extension. Gemini CLI lists what the extension adds and asks before it goes on.

The terminal shows gemini extensions install listing the faxforagents MCP server the extension adds and asking whether to continue.
Run gemini extensions install with the extension address. Gemini CLI lists the faxforagents tool server and asks "Do you want to continue?". Type Y.

2.Paste your API key

The extension declares one setting, your Fax for Agents API key. Gemini CLI asks for it once, during the install, and keeps it in your system keychain.

Gemini CLI asks for the Fax for Agents API key during the install, with a masked input line.
Paste your Fax for Agents API key when Gemini CLI asks. The input is masked. The install ends with "Extension "faxforagents" installed successfully and enabled."

3.Choose the API key

Start Gemini CLI with gemini -m gemini-3.5-flash-lite. On the first start it asks how to authenticate.

Gemini CLI asks how to authenticate, with Use Gemini API Key selected and the note Existing API key detected (GEMINI_API_KEY).
With GEMINI_API_KEY set in your shell, "Use Gemini API Key" is already selected and Gemini CLI says "Existing API key detected (GEMINI_API_KEY)". Press Enter. The next dialog, "Enter Gemini API Key", already holds your key, shown as asterisks. Press Enter again.

4.Gemini CLI is ready

Gemini CLI at its prompt, the footer showing 1 GEMINI.md file and 1 MCP server.
The footer shows "1 MCP server". That is the Fax for Agents tool server from the extension.

5.Allow the fax tools

Type what the fax should say and where it goes. Gemini CLI asks once before it runs a tool from the extension.

Gemini CLI asks Allow execution of MCP tool prepare_fax from server faxforagents, with three Allow options and No, suggest changes.
Choose "Allow all server tools for this session". Gemini CLI stops asking for the rest of the session. "Allow once" and "Allow tool for this session" work too, with more prompts.

6.Send it

Gemini prepares a one page document from your words, asks for a quote and sends it. The send goes through at once because the quote is inside your limits.

Gemini reports the fax to +15550000001 as sent, with the fax id and the quote id.
Gemini quotes the page and sends it at once. It reports "Fax sent to +1 555 000 0001 and delivered successfully" with the fax id.

7.Check the evidence

Ask for the delivery evidence when you want the full record.

The delivery evidence for the fax: state delivered, the provider reference, remote station SBX-OK, pages delivered and the time completed.
Gemini answers with the state, the provider reference, the remote station SBX-OK, the pages sent, the duration and the time completed. SBX-OK is the sandbox carrier's reply.

8.Read the inbox

Received faxes work the same way. Ask for your inbox.

Gemini lists the inbox and prints the text of the newest received fax from +15550000042, two pages.
Gemini lists the received faxes and reads the newest one as text, with the sender's number and the page count.

What the limits mean

Open Settings in the dashboard. The Connected apps card holds the switch "Let connected apps send without asking". Under it are two fields, "Amount per fax, at most" ($5.00) and "Faxes per day" (20). A connected app key, like the one in this guide, sends inside these limits with no approval per fax. Turn the switch off and every send waits for a person. Finer limits, such as destinations or one app only, live under Policies. See the guide Your assistant sends within limits by default.

Approve every fax instead

  1. In Settings, turn off "Let connected apps send without asking" and choose Save.
  2. Ask Gemini to quote the fax. The quote says approval is required.
  3. Say "Ask a person to approve it." A person approves in the dashboard or with the ffa command line, then you tell Gemini to send.

The full routine is in Approve every fax from Gemini CLI.

Troubleshooting

  • Gemini CLI sits on "Thinking..." for minutes after the first prompt. The default model of Gemini CLI 0.62 is not open to new API keys and the CLI retries quietly. Start it with a current model, for example gemini -m gemini-3.5-flash-lite.
  • A dialog says "Usage limit reached" and offers another model. A free API key has a low number of requests per minute, and a fax turn makes several calls. The lite models allow more. Choose Stop, wait a minute, and ask again.
  • Gemini asks "Allow execution of [Shell]?" and wants to run a command instead of using the fax tools. Choose "No, suggest changes" and add a GEMINI.md to the folder that names the faxforagents tools, as under Before you start.
  • The quote says "deny" or "approval required" although you expect a plain send. An owner turned the Connected apps switch off, or the fax is above a limit. Check Settings, Connected apps for your environment.

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