For developers and AI agents

A chargeback MCP server.

Chargeback knowledge is exactly the shape an agent should be able to ask for: a code goes in, the required evidence and the deadline come out. So we are exposing ours over the Model Context Protocol rather than making a person read a PDF.

Reference API live now. MCP wrapper in progress.

What it exposes

Backed by a structured database of 63 reason codes across Visa, Mastercard, American Express and Discover, each carrying its required evidence, recommended evidence, response window and win-probability factors.

Free, no key — live today over HTTPS

Reference lookups stay open. An agent should not need an account to find out that a Visa 10.4 response is due in 30 days. The same data the MCP tools will return is already served as JSON with CORS enabled:

GET https://feefighters.com/api/v1/reason-codes          # all 63, summary
GET https://feefighters.com/api/v1/reason-codes/10.4     # one code, full record
GET https://feefighters.com/api/v1/reason-codes/visa     # every code for a network

lookup_reason_code(code)

The full record for a network reason code: category, response window, required and recommended evidence, win strategy, win-probability factors.

evidence_checklist(code)

What that specific code requires, split required and recommended, each item with plain-language help text.

compute_deadline(code, dispute_date)

Response deadline and urgency level. Flags an estimated deadline as estimated.

assess_win_probability(code, evidence_held)

An honest assessment given the evidence actually in hand, including when the answer is to accept the loss.

list_codes_by_network(network)

Enumerate the codes for visa, mastercard, amex or discover.

With an API key

Included with any paid plan.

create_dispute

Open a dispute and start evidence collection.

upload_evidence

Attach a document or text value against an evidence key.

generate_response_package

Rebuttal letter, labelled exhibits, transaction summary and the submission guide for that processor.

portfolio_ratio

Dispute and fraud ratio across a portfolio of MIDs, measured against VAMP thresholds.

Once it ships

{
  "mcpServers": {
    "feefighters": {
      "command": "npx",
      "args": ["-y", "@feefighters/mcp"]
    }
  }
}

Discovery manifest lives at /.well-known/mcp.json. A plain-language site summary for models is at /llms.txt.

Why we are doing this

The merchant who gets a chargeback notice rarely knows what a reason code is. But the ops team at an ISO does, the engineer wiring up a payments platform does, and increasingly the agent acting for either of them does. Reference data that answers a machine's question is worth more open than locked.

The paid product is everything after the lookup: evidence collection, the drafted rebuttal, the assembled package and the portfolio view.

Early access

Tell us what you would call and we will build against it. Portfolio owners and payments platforms go to the front of the queue.

If you want the underlying data another way — a REST endpoint, a bulk export of the reason-code database — say so. We would rather it be used than admired.