onyx-paid-mcp — build a paid MCP server in 5 lines

USDC settlement on Base. No Stripe, no API keys, no signup flow. Charge AI agents per call directly through the protocol they already speak.

from onyx_paid_mcp import App

app = App(
    name="hello-paid-mcp",
    receive_address="0xYourBaseWallet",
    network="base",   # or "base-sepolia" for free testnet
)

@app.tool(
    name="echo",
    price_usdc="0.001",
    description="Returns whatever you send.",
    input_schema={"type": "object", "properties": {"text": {"type": "string"}}, "required": ["text"]},
)
def echo(text: str) -> dict:
    return {"echoed": text}

if __name__ == "__main__":
    app.serve(port=8080)

That's it. pip install onyx-paid-mcp, point at any wallet address, decorate any function. You now have:

• Streamable HTTP MCP at /mcp/ — installable in Claude Desktop, Cursor, Cline, mcp-use
• REST endpoint at /v1/<tool> — for non-MCP agents
• HTTP 402 gate that charges your wallet per call in USDC
• Bazaar-discoverable manifest at /.well-known/x402.json — Coinbase auto-indexes
• Free introspection at /, /manifest, /health

Why

Every MCP today is free-as-in-unmetered. That breaks at scale for any tool with real per-call expense (OCR, scraping infra, LLM passes, anything backed by a physical resource). onyx-paid-mcp lets you charge directly through the agent's wallet — the same way a paywall works in a browser, except the wallet signs an EIP-3009 USDC authorization instead of pulling out a credit card.

Install

pip install onyx-paid-mcp

Generate a Base wallet (gen_wallet.py in this repo, or any EVM wallet generator), set it as ONYX_RECEIVE, run your tool. Agents pay you in USDC the second they call.

Reference implementation

onyx-actions — the live server using this framework. Paid tools across Base on-chain primitives, captcha OCR, URL text extraction, DNS, WHOIS, email validation, IP geo, FX, browser automation, and a workflow chainer. All shipped as one-file modules in tools_pkg/.

Tool	Price
onyx_base_tx_explainer	$0.05
onyx_base_tx_simulator	$0.10
onyx_base_token_risk_scan	$0.25
onyx_base_tx_decode	$0.002
onyx_token_metadata	$0.001
onyx_solana_tx_explainer	$0.05
onyx_solana_token_metadata	$0.0008
onyx_solana_token_risk_scan	$0.25
onyx_solana_jupiter_quote	$0.001
onyx_solana_wallet_activity	$0.002
onyx_ens_resolve	$0.0008
onyx_solve_captcha	$0.003
onyx_url_text	$0.001
onyx_url_unshorten	$0.0005
onyx_whois	$0.001
onyx_dns_lookup	$0.0005
onyx_email_validate	$0.0008
onyx_ip_geolocate	$0.0008
onyx_fx_convert	$0.0008
onyx_password_strength	$0.0003
onyx_user_agent_parse	$0.0003
onyx_browser_* (6 tools)	$0.002–$0.008
onyx_agent_workflow	$0.020

Smithery listing: https://smithery.ai/servers/dimitrilaouanis/onyx-mcp

Integrations in flight

• Stagehand (Browserbase) — pay-per-call captcha hook over x402. Spec: BROWSERBASE_INTEGRATION.md. Discussion: #1.

How agents call you

Try it against the live reference server with one command — no install:

curl -X POST https://onyx-actions.onrender.com/v1/onyx_solana_jupiter_quote \
  -H "content-type: application/json" \
  -d '{"input_mint":"So11111111111111111111111111111111111111112","output_mint":"EPjFWdd5AufqSSqeM2qN1xzybapC8G4wEGGkZwyTDt1v","amount":"1000000000"}' -i
# → HTTP 402 Payment Required
# → payment-required: <base64-encoded JSON with payTo, asset, amount, inputSchema>

Then sign an EIP-3009 USDC authorization and retry with X-PAYMENT: <signed>:

# Full client demo — shows the 402 → sign → 200 loop in 50 lines:
python examples/agent_pay.py onyx_solana_jupiter_quote
# Set ONYX_DEMO_KEY=0x... to actually pay + get the result

Any x402-aware client SDK (Coinbase CDP, Cloudflare Agent SDK, Privy, mcp-use) handles the loop in ~5 lines. Agents don't need to know your URL — the Coinbase Bazaar crawler picks up your /.well-known/x402.json from on-chain settled payments.

Configure

The framework defaults are sane. Customize via constructor or env:

Field	Default	Note
name	required	shows up in MCP, manifest, landing page
receive_address	required	where USDC settles
network	base-sepolia	or base for mainnet
facilitator_url	x402.org public	swap for Coinbase CDP / xpay / your own
public_url	None	sets the canonical URL in manifests
description	empty	short one-liner
homepage	None	optional landing page URL

Self-hosting checklist

1. Generate or pick a Base wallet (just an address — private key never leaves your machine; this is a receive-only flow)
2. Funded wallet not required to receive — only senders need USDC
3. Pick a host: Render free tier works; Fly.io machines for always-on; Cloudflare Tunnel + Oracle ARM for zero-cost-zero-cold-start
4. pip install onyx-paid-mcp, write your app.py, deploy
5. Submit https://your-server/.well-known/x402.json to Coinbase Bazaar — first settled payment auto-indexes you everywhere

Status

v0.1.0 — released April 2026. Battle-tested on onyx-actions.onrender.com (live since Apr 24).

License

MIT — see LICENSE.