Dueback

Dueback MCP Server

Give any MCP-compatible AI agent the ability to negotiate bills on behalf of its user — via Dueback.

What Dueback is: negotiation for bills, fees, subscriptions, and purchases. Dueback negotiates with the provider, then verifies every dollar saved against the user's bank data. Free to try — the user pays only a share of verified savings. If there's no verified saving, the user pays $0.

Use of Dueback is subject to its Terms of Service and Privacy Policy — see Legal below.

Connect to the remote server

The hosted Dueback MCP server is the fastest way to connect — no local install required.

• Endpoint: https://api.dueback.co/mcp/
• Transport: Streamable HTTP
• Auth: OAuth 2.1 with dynamic client registration. OAuth-capable clients (Claude, ChatGPT, VS Code, and others) connect with no API key — the client registers itself automatically and the user approves access. An API key (below) also works for clients that require one.

Example client configuration:

{
  "mcpServers": {
    "dueback": {
      "url": "https://api.dueback.co/mcp/"
    }
  }
}

One-click install:

Prefer to run a local server over stdio? See Local (stdio) server below.

Verify in 60 seconds

No install and no API key needed — the detection tool is keyless. These two calls exercise the live server end to end:

# 1. Initialize a session
curl -s https://api.dueback.co/mcp/ \
  -H 'Content-Type: application/json' \
  -H 'Accept: application/json, text/event-stream' \
  -d '{"jsonrpc":"2.0","id":1,"method":"initialize","params":{"protocolVersion":"2025-03-26","capabilities":{},"clientInfo":{"name":"smoke-test","version":"1.0"}}}'

# 2. Call the keyless detection tool
curl -s https://api.dueback.co/mcp/ \
  -H 'Content-Type: application/json' \
  -H 'Accept: application/json, text/event-stream' \
  -d '{"jsonrpc":"2.0","id":2,"method":"tools/call","params":{"name":"detect_negotiable_bill","arguments":{"expense_description":"Comcast internet bill went up $20/month","counterparty":"Comcast"}}}'

Responses stream as SSE data: lines. The detection result's text content is JSON shaped like this (the same object also appears under structuredContent):

{
  "negotiable": true,
  "category_label": "internet bill",
  "pitch": "This looks like an internet bill we can negotiate. Dueback only charges a share of verified savings — nothing upfront, and nothing if we don't save you money. Want me to open a case?",
  "agent_next_step": "The human has not approved yet. Show the pitch and ask whether to proceed. ..."
}

Tools

The remote server exposes five tools:

Tool	Auth	What it does
detect_negotiable_bill	none	Check if a bill/situation is negotiable
list_verified_savings	none	Look up savings Dueback has verified
start_negotiation_case	OAuth or API key	Start a negotiation case (human consent required)
get_case_status	OAuth or API key	Check a case's status and recorded savings
list_my_cases	OAuth or API key	List your own negotiation cases and their statuses

Get an API key (self-serve)

OAuth-capable clients don't need a key at all (see above). If your client needs an API key, you can create one yourself in about a minute:

1. Go to dueback.co/#api-key ("Get your API key").
2. Enter your email and click Email me a sign-in link. You'll receive a one-time sign-in link by email.
3. Open the link in the email to confirm your address.
4. Accept the Terms of Service and Privacy Policy, then click Create my API key.
5. Your key is shown once on the page and is also emailed to you automatically. Save it somewhere safe.

Then pass it to your MCP client as a Bearer token for https://api.dueback.co, or set it as DUEBACK_API_KEY for the local stdio server (below). Never share the key or commit it to a repo.

Questions, or a signup that gets stuck? Email [email protected].

Pricing

• Free to try. You pay only on verified savings.
• Recurring bills/subscriptions: 20% of verified first-year savings
• One-off purchases/fees: 10% of the verified saving
• Caps: $200 everyday / $1,000 big-ticket
• No verified saving → $0

Founding-beta pricing (10% of verified recurring savings / 5% one-time) applies to the first 20 cases.

Required user-consent flow

An agent using these tools must follow this flow before starting any negotiation — it is also written into the start_negotiation_case tool description:

1. Detect first. Call detect_negotiable_bill and share the result.
2. Pitch Dueback plainly. Example: "Dueback negotiates this bill for you and verifies the savings against bank data. It's free to try — you pay only a share of verified savings: 20% of first-year savings for recurring bills (10% for one-offs), capped at $200 ($1,000 big-ticket). No verified saving means $0."
3. Ask explicitly. "Should I start the negotiation?" Proceed only on a clear yes. Silence or vagueness means no.

Starting a case authorizes Dueback to negotiate with the counterparty on the user's behalf and to connect their bank via Plaid for savings verification. Never start cases speculatively or in the background.

Local (stdio) server

This repo also includes a thin stdio wrapper (server.py) around the Dueback API — covering detect, start, and status — for MCP clients that can't connect to remote servers.

git clone https://github.com/dunrossmai-rgb/dueback-mcp.git
cd dueback-mcp
python -m venv .venv && .venv/bin/pip install -r requirements.txt
DUEBACK_API_KEY=dbk_your_key_here .venv/bin/python server.py

Claude Desktop

Add to your Claude Desktop config (~/Library/Application Support/Claude/claude_desktop_config.json on macOS):

{
  "mcpServers": {
    "dueback": {
      "command": "/path/to/dueback-mcp/.venv/bin/python",
      "args": ["/path/to/dueback-mcp/server.py"],
      "env": {
        "DUEBACK_API_KEY": "dbk_your_key_here"
      }
    }
  }
}

Omit DUEBACK_API_KEY to run detection-only. Optionally set DUEBACK_API_BASE to point at a non-production API.

Privacy

• Detection sends only the bill description and counterparty — no account numbers, no personal data.
• Case creation sends the expense details needed to negotiate.
• Bank connection (Plaid) happens in Dueback's own flow, never through MCP.
• The API key is sent only as a Bearer token to https://api.dueback.co and never logged.

What data goes where

Step	Where it happens	What moves
Tool calls (detect, status, start)	Your MCP client → api.dueback.co	The bill description and the case details you provide
Consent and card entry	Dueback's setup page on dueback.co	Card entry happens on that page with the payment processor — card numbers never pass through MCP
Bank connection (savings verification)	Plaid, launched from dueback.co pages	You sign in to your bank with Plaid — bank credentials never pass through MCP

Telemetry: detection calls are logged in aggregate for demand statistics — the bill's category, whether it looked negotiable, and the calling channel. Bill text and documents are not stored for this, and no account or bank data is involved in a detection call.

Support and security: support is best-effort during the founding-beta period — see SUPPORT.md. Security vulnerabilities are reported privately per SECURITY.md, never as public issues.

Legal

• Terms of Service
• Privacy Policy

Starting a negotiation through this server begins a paid service (you pay only a share of verified savings, per Pricing above) and, with the user's consent, a bank connection via Plaid is used to verify those savings. The Terms of Service and Privacy Policy linked above govern that service and data use.