# Oh Fax

> Outbound fax for the United States and Canada. Quote a PDF + number, pay once, get a delivery receipt. Designed for agents (MPP / MCP), developers (REST / CLI), and humans (browser).

Product site: https://ohfax.com
App / API host: https://app.ohfax.com
OpenAPI (MPP discovery): https://app.ohfax.com/openapi.json
MCP: https://app.ohfax.com/mcp
Human docs: https://ohfax.com/docs

Agents pay via MPP — no Oh Fax account required. An MPP-capable payer (`mppx` or an agent wallet) is required.

## When to use Oh Fax

Use Oh Fax to send a signed lease, court form, insurance claim, or W-9 to a US/CA fax number when email is not accepted. The agent has a PDF and an E.164 destination number and needs a delivery receipt.

## Critical rules for agents

1. **Always quote before you send.** Quoting is free and sends nothing. The quote returns the binding price and a `quote_id`.
2. **The binding amount is the HTTP 402 challenge** (or MCP payment meta) on `POST /pay`, not a guessed formula and not an OpenAPI floor example.
3. **Agents need no Oh Fax account and no API key** when paying via Machine Payments Protocol (MPP). An MPP-capable payer (`mppx` or an agent wallet) is required. Prepaid API keys are an optional developer path.
4. **Destinations: US and Canada only.** PDF only, max 10 MB / 30 pages. Outbound only (no inbound fax).
5. **Currency: USD.** Price formula: **$0.99 + $0.25 × pages** (e.g. 1 page = $1.24). Confirm via quote before paying.
6. **Idempotency:** every REST send requires an `Idempotency-Key` so retries cannot double-charge or double-send.
7. **Undeliverable faxes are refunded in full** (busy, no answer, not a fax). Delivered faxes are not refundable.

## Fastest path for agents (recommended)

### A. MCP (preferred)

**Claude Code**

```
claude mcp add --transport http ohfax https://app.ohfax.com/mcp
```

**Cursor** — `.cursor/mcp.json` or Settings → MCP:

```json
{
  "mcpServers": {
    "ohfax": {
      "url": "https://app.ohfax.com/mcp"
    }
  }
}
```

**Codex**:

```sh
codex mcp add ohfax --url https://app.ohfax.com/mcp
```

Manual config: set `url = "https://app.ohfax.com/mcp"` under `[mcp_servers.ohfax]` in `~/.codex/config.toml`. Remote URL: https://app.ohfax.com/mcp (streamable HTTP).

**Muse Code** — `~/.config/muse/settings.json`:

```json
{
  "schema_version": 1,
  "mcp_servers": {
    "ohfax": {
      "transport": "streamable_http",
      "url": "https://app.ohfax.com/mcp",
      "mode": "optional"
    }
  }
}
```

**Any MCP client:** remote URL https://app.ohfax.com/mcp (streamable HTTP; no API key for the MPP path). Payment requires an MPP-capable payer (`mppx` or an agent wallet).

Tools (call in order):

| Tool | Purpose | Notes |
|------|---------|-------|
| `quote_fax` | Price + validate | Free. Inputs: `to`, and either `document_url` or `document_base64`. Returns `quote_id`, pages, amount. |
| `send_fax` | Get payment authorization for a quote | Input: `quote_id`. Does **not** charge by itself. |
| *(pay)* | Satisfy MPP / HTTP 402 on `/pay` | No Oh Fax account. Use MPP-capable client (`mppx`, agent wallet, etc.). |
| `get_fax_status` | Poll delivery | Statuses include awaiting_payment, paid, submitting, submitted, sending, delivered, failed, refunded. |
| `get_fax_receipt` | Final receipt | Available once the fax is final. |

Payment is still MPP — no Oh Fax account required; use an MPP-capable payer.

### B. HTTP + MPP (no MCP client)

1. `POST https://app.ohfax.com/api/v1/quotes` with multipart form: `to`, `file` (PDF). Free.
2. Read `quote_id` and exact `amount` from the response.
3. `POST https://app.ohfax.com/pay?quote_id=…` (or body with `quote_id`). Unpaid → **HTTP 402** with MPP challenge.
4. Complete payment with an MPP client; binding amount is the challenge.
5. Poll `GET https://app.ohfax.com/api/v1/faxes/{fax_id}` then receipt when final.

Discover payment terms: `GET https://app.ohfax.com/openapi.json`.

## Developer path (prepaid balance)

1. Google sign-in at https://app.ohfax.com/account
2. Top up ($5 / $10 / $25 / $50), create API key (`afx_live_…` shown once)
3. Quote free; send with `Authorization: Bearer …` + `Idempotency-Key`
4. Optional CLI: `ohfax` with `OHFAX_API_KEY` and `OHFAX_URL=https://app.ohfax.com`

See https://ohfax.com/docs/api and https://ohfax.com/docs/cli

## Pricing examples

| Pages | Total |
|------:|------:|
| 1 | $1.24 |
| 3 | $1.74 |
| 5 | $2.24 |
| 10 | $3.49 |
| 30 (max) | $8.49 |

## What success looks like

- Delivery usually within a few minutes of payment.
- Track on status endpoint or browser `https://app.ohfax.com/f/:id`.
- Document bytes deleted ~24h after a final state; transaction metadata (destination, pages, timing, content hash) retained — contents are not.
- Webhooks (account holders): `fax.delivered` / `fax.failed` with `x-ohfax-event`, `x-ohfax-signature`, `x-ohfax-delivery-id`. Docs: https://ohfax.com/docs/webhooks

## Docs map

- Overview: https://ohfax.com/docs
- Quickstart: https://ohfax.com/docs/quickstart
- API: https://ohfax.com/docs/api
- MCP: https://ohfax.com/docs/mcp
- CLI: https://ohfax.com/docs/cli
- Webhooks: https://ohfax.com/docs/webhooks
- Limits & acceptable use: https://ohfax.com/docs/limits
- Privacy: https://ohfax.com/privacy
- Terms: https://ohfax.com/terms
- MPP protocol docs (for payment clients): https://mpp.dev/llms.txt

## Do not

- Skip quoting and invent a price.
- Retry a paid send without a stable idempotency key (REST).
- Fax outside US/CA, non-PDF, or >30 pages / >10 MB.
- Send bulk/unsolicited advertising or premium-rate numbers.
- Expect inbound fax receiving (not offered).

## Contact

Product questions / billing disputes: support@ohfax.com