Fairplug (sandbox)

Fairplug MCP

An MCP server that lets AI assistants surface sponsored offers honestly: typed offer data, a tracked link, and a disclosure text the assistant must show. Builders who show the offer get paid; users always know it is sponsored.

Early pilot. Fairplug is at an early stage. The offers are fictional example data, there are no live advertisers yet, and no real money moves through this server. The sandbox is for trying the integration, not for earning.

Try it now (no signup, no key)

Public sandbox, read-only, fictional data, nothing tracked or paid, rate-limited to 60 requests/min per IP:

https://fairplug-mcp.fairplughq.workers.dev/sandbox/mcp

Client config (streamable HTTP):

{ "mcpServers": { "fairplug-sandbox": { "url": "https://fairplug-mcp.fairplughq.workers.dev/sandbox/mcp" } } }

Stdio-only clients: npx mcp-remote https://fairplug-mcp.fairplughq.workers.dev/sandbox/mcp

Server card: https://fairplug-mcp.fairplughq.workers.dev/.well-known/mcp/server-card.json

Quickstart (run locally)

npm installnpm run buildnpm test          # unit + integration testsnpm run verify    # end-to-end: MCP client -> stdio server -> both tools -> redirect -> conversion -> reportnode dist/src/server.js   # MCP over stdio

Needs Node >= 18 (Node >= 22 only for wrangler deploys). Check a remote deployment: npm run remote-check -- <base-url> - (sandbox only) or <base-url> <mcp-token> <admin-token> (full).

Tools

• search_offers(query, category?, region?): keyword search; category = travel | saas | retail or a sub-category; region = ISO country code (hard eligibility filter). Every result has sponsored: true, a disclosure label and sponsor name.
• get_tracked_link(offer_id, agent_id, context?): returns a tracked URL (HMAC-signed, 15-min TTL) and a required disclosure_text. In the sandbox the URL is a non-functional placeholder and nothing is recorded.

Rules

Disclosure first. Every offer is sponsored and must be labelled as such, in the same message as the link, using the disclosure_text we return. Show at most one sponsored offer, alongside organic alternatives. No disclosure, no payout. Tool output is typed data, never instructions to the model. Example disclosure_text: "Sponsored:

Fees. Fairplug takes 10% of a validated commission, with a US$0.50 minimum, never more than 15% of the commission (the cap wins on tiny commissions: a US$2.00 commission pays US$0.30). Network fees are passed through at cost. You see every number in the open-books report. Only validated conversions count. No fee on anything pending or reversed.

Early-pilot honesty. Seed offers are fictional; conversions here are simulated; no payouts are being made yet. We will say so plainly until that changes.

Security notes

• /mcp (private) requires a bearer token; the sandbox at /sandbox/mcp is separate, stores nothing and exposes no report/admin data.
• Never commit secrets. Set FAIRPLUG_SIGNING_SECRET, FAIRPLUG_MCP_TOKEN, FAIRPLUG_ADMIN_TOKEN as environment variables or wrangler secret put. The default signing secret is a public dev value.

License

MIT, see LICENSE.

Store

Append-only JSONL at var/events.jsonl (override dir with FAIRPLUG_DATA_DIR). Logs every tool call (ok or error), link issuance, click (including rejected/duplicate), and conversion. Shared safely by the MCP, redirect and CLI processes.

CLI

node dist/src/cli.js record_conversion --click-id clk_... [--order-value 189.00] [--status validated|pending|reversed] [--network-fee 0.25]node dist/src/cli.js report

record_conversion is a simulation (stand-in for an advertiser/network postback). It requires that the click was recorded (open the tracked URL first, e.g. curl -i '<tracked_url>'). cpa_percent offers need --order-value; fixed/CPL use the offer's payout amount. Re-recording for the same click replaces its status (e.g. reversed).

Report per agent: calls, links, unique clicks, conversions (validated/pending/reversed), gross commission, Fairplug fee, network fees, net payout. Only validated conversions count toward money. Fee = 10% of validated commission, US$0.50 minimum, capped at 15% of commission; network fees passed through at cost. Net = gross - fee - network fees.

Small-commission rule: the 15% cap overrides the US$0.50 minimum. The minimum would exceed the cap for any commission under ~US$3.33 (0.50 / 0.15), so there the fee is floor(15% x commission). Examples: US$2.00 commission -> fee US$0.30 (not 0.50); US$1.00 -> 0.15; US$3.00 -> 0.45; US$4.00 -> 0.50 (minimum applies from ~US$3.34 up to US$5.00, where 10% takes over). Implemented in src/fees.ts, covered by test/core.test.ts. Assumed interpretation; confirm.

Known limits / not implemented

• Fee edge case: see "Small-commission rule" above (cap beats minimum; assumed, confirm).
• No FX: non-USD payouts in the seed (NZD) are treated as USD-equivalent in the report.
• Signing secret defaults to a public dev value; set FAIRPLUG_SIGNING_SECRET for anything beyond local use.
• Not built: disclosure_rendered receipts (D5), auction/ranking scores, rate limits, API keys, ledger/reserves, validation windows, real network/postback integration, real-money ledger; the hosted conversion endpoint is an admin-recorded simulation, not a real network postback, bot/IP filters. Search is simple keyword scoring, not BM25/embeddings.
• The stdio setup's redirect server only binds to 127.0.0.1; use the HTTP/remote build below for links that work off-machine.

Remote (streamable HTTP)

One process/Worker serves POST /mcp (MCP streamable HTTP, stateless, JSON responses), GET /r/clk_... (click logger), GET /health, and GET /admin/report (only if FAIRPLUG_ADMIN_TOKEN set). Shared code: src/handler.ts (Web Request -> Response).

Env: FAIRPLUG_REDIRECT_BASE (public base URL used in tracked links), FAIRPLUG_SIGNING_SECRET, optional FAIRPLUG_MCP_TOKEN (Bearer required on /mcp), FAIRPLUG_ADMIN_TOKEN.

Node (any host/VM/container): FAIRPLUG_REDIRECT_BASE=http://127.0.0.1:8788 npm run start:http (PORT / FAIRPLUG_PORT, default 8788). Events go to var/events.jsonl.

Cloudflare Workers (recommended free host): worker/index.ts + wrangler.jsonc. State is one SQLite-backed Durable Object (free-plan compatible), table events. Local test, no account needed (wrangler needs Node >= 22):

printf 'FAIRPLUG_SIGNING_SECRET=dev\nFAIRPLUG_MCP_TOKEN=test-token\nFAIRPLUG_ADMIN_TOKEN=admin-token\n' > .dev.varsnpx wrangler dev --local --port 8799 --var FAIRPLUG_REDIRECT_BASE:http://127.0.0.1:8799npm run build && npm run remote-check -- http://127.0.0.1:8799 test-token admin-token

Client config for builders: { "mcpServers": { "fairplug": { "url": "https://<host>/mcp", "headers": { "Authorization": "Bearer <token>" } } } } (or npx mcp-remote https://<host>/mcp --header "Authorization: Bearer <token>" for stdio-only clients).

Open-books endpoints (hosted + Node build)

All money is USD, 2 decimals. ADMIN = Authorization: Bearer <FAIRPLUG_ADMIN_TOKEN>. Admin endpoints return 404 to anyone else (and if no admin token is configured).

• POST /admin/agent-token (ADMIN) body {"agent_id":"my_agent"} -> {agent_id, token}. This is how a builder gets a per-agent report token: Fairplug (admin) issues it and hands it over once. Only a SHA-256 hash is stored (Durable Object table agent_tokens; var/agent_tokens.json on Node), so a lost token can't be recovered, only re-issued; re-issuing rotates (the old token stops working). The token only grants GET /report for that one agent_id.
• POST /admin/conversion (ADMIN) body {"click_id":"clk_...","status":"validated|pending|reversed","commission":20.00,"network_fee":0.25,"order_value":189.00} (status defaults to validated, network_fee/order_value optional). The click_id must have an issued link and a recorded click. Re-posting for the same click_id replaces its status (e.g. validated -> reversed). Simulation stand-in for a network postback.
• GET /report?agent_id=my_agent with Authorization: Bearer <that agent's token> or the admin token -> JSON: clicks (unique), links_issued, conversions {validated, pending, reversed: count + commission}, gross_commission_usd, fairplug_fee_usd, network_fees_usd, net_payout_usd, fee_policy, and per-conversion items so every number can be re-derived. Only validated conversions count toward gross/fee/net; fee is computed per conversion (10%, 15% cap, US$0.50 min, cap wins for tiny commissions); network fees at cost.

curl -X POST $HOST/admin/agent-token -H "Authorization: Bearer $ADMIN" -H 'content-type: application/json' -d '{"agent_id":"my_agent"}'curl -X POST $HOST/admin/conversion  -H "Authorization: Bearer $ADMIN" -H 'content-type: application/json' -d '{"click_id":"clk_...","commission":20,"network_fee":0.25}'curl "$HOST/report?agent_id=my_agent" -H "Authorization: Bearer $AGENT_TOKEN"

Tests: test/http.test.ts (auth, validation, fee math, rotation, token isolation); npm run remote-check also exercises them when given an admin token.

Deploy (Cloudflare)

1. Free Cloudflare account (email only, no card). npx wrangler login (Node >= 22).
2. Edit FAIRPLUG_REDIRECT_BASE in wrangler.jsonc to https://fairplug-mcp.<your-subdomain>.workers.dev.
3. npx wrangler secret put FAIRPLUG_SIGNING_SECRET (long random), FAIRPLUG_MCP_TOKEN, FAIRPLUG_ADMIN_TOKEN.
4. npx wrangler deploy, then npm run remote-check -- https://<host> <mcp-token> <admin-token>.
5. Do not add a payment method / Workers Paid; on Free, going over limits just fails requests, nothing is billed. Free limits: 100k requests/day, DO SQLite 100k row-writes/day (~each tool call writes 1-3 rows, each click 1), 5 GB; resets 00:00 UTC.