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Lightning-paywall sidecar: wraps any stdio MCP server, requires paid invoices before tool calls.
Lightning-paywall sidecar: wraps any stdio MCP server, requires paid invoices before tool calls.
paywall-mcp is a well-architected Lightning payment gateway for MCP servers with strong security fundamentals. Authentication and payment verification logic is sound, input validation is comprehensive via Zod schemas, and dangerous operations (shell execution, file I/O) are appropriately scoped. The server properly isolates secrets via environment variables and includes audit logging. Minor code quality observations around error handling and NWC dependency trust do not materially impact security. Supply chain analysis found 5 known vulnerabilities in dependencies (2 critical, 2 high severity). Package verification found 1 issue.
7 files analyzed · 11 issues found
Security scores are indicators to help you make informed decisions, not guarantees. Always review permissions before connecting any MCP server.
This plugin requests these system permissions. Most are normal for its category.
Set these up before or after installing:
Environment variable: PAYWALL_UPSTREAM_COMMAND
Environment variable: PAYWALL_UPSTREAM_ARGS
Environment variable: NWC_CONNECTION_STRING
Environment variable: PAYWALL_DEFAULT_PRICE_SATS
Environment variable: PAYWALL_PRICE_MAP
Add this to your MCP configuration file:
{
"mcpServers": {
"io-github-llmops-pro-paywall-mcp": {
"env": {
"PAYWALL_PRICE_MAP": "your-paywall-price-map-here",
"NWC_CONNECTION_STRING": "your-nwc-connection-string-here",
"PAYWALL_UPSTREAM_ARGS": "your-paywall-upstream-args-here",
"PAYWALL_UPSTREAM_COMMAND": "your-paywall-upstream-command-here",
"PAYWALL_DEFAULT_PRICE_SATS": "your-paywall-default-price-sats-here"
},
"args": [
"-y",
"paywall-mcp"
],
"command": "npx"
}
}
}From the project's GitHub README.
Paywall ANY stdio MCP server with Lightning, without modifying it. paywall-mcp is a generic sidecar: configure it with an upstream MCP server command and a per-tool price map, and it transparently:
tools/list from the upstream to the LLM client, with prices appended to each tool's description.tools/call: free tools pass through; priced tools require a paid Lightning invoice (via Nostr Wallet Connect / NIP-47) before the call is forwarded.No code changes to the upstream server. Works with Anthropic's reference MCP servers, your own, or any third-party MCP server that speaks stdio.
v0.1 — proxy + payment gate complete. Spawns a stdio upstream as a child process; per-tool pricing via env; in-memory invoice cache + replay protection; audit log; read-only mode. Persistent cache + HTTP/SSE upstream transport deferred to v0.2.
Modern paid-API patterns (Lightning paywall, L402, micropayments) exist for HTTP but the MCP ecosystem has no standard for paid tool calls. Building it into each individual server is repetitive and error-prone. paywall-mcp is the missing sidecar: write your tools as a normal MCP server, then wrap it with paywall-mcp to charge sats per call.
For any priced tool:
priced_tool({...args}) without payment_hash. paywall-mcp issues a bolt11 invoice through your NWC wallet and returns:
{
"error": "payment_required",
"invoice": "lnbc...",
"payment_hash": "abc123...",
"amount_sats": 21,
"expires_in_seconds": 600,
"next_step": "Pay this bolt11 ..."
}
nwc-mcp — the same LLM can call nwc_pay_invoice to settle.priced_tool({...args, payment_hash: "abc123..."}). paywall-mcp verifies settlement via NWC lookup_invoice, strips payment_hash from the args, forwards the original call to the upstream, returns the upstream's result.Replay protection: the same payment_hash cannot be redeemed twice. Buyers pay a fresh invoice for each call.
free_lookup: 0, premium_analysis: 100, rare_alpha_signal: 5000. Buyers see prices in tool descriptions.PAYWALL_PRICE_MAP in env, restart, you're at the new price.make_invoice + lookup_invoice are the only permissions paywall-mcp needs. A receive-only NWC connection is perfectly fine and recommended — paywall-mcp never spends.# From npm
npx -y paywall-mcp
# From source
git clone <repo>
cd paywall-mcp
corepack enable pnpm
pnpm install
pnpm build
cp .env.example .env
# edit .env: set PAYWALL_UPSTREAM_COMMAND/ARGS, NWC_CONNECTION_STRING, prices
The server auto-loads .env from its own directory (next to dist/) — deliberately NOT from cwd, to avoid env collisions when running multiple MCP servers in the same Claude Code session.
| Var | Purpose |
|---|---|
PAYWALL_UPSTREAM_COMMAND | Executable to spawn as the upstream MCP server (e.g., node). |
PAYWALL_UPSTREAM_ARGS | JSON array of args passed to the upstream command (e.g., ["/path/to/upstream/dist/index.js"]). |
| Var | Purpose |
|---|---|
NWC_CONNECTION_STRING | NIP-47 NWC URI for the seller's RECEIVE wallet. make_invoice + lookup_invoice permissions sufficient. paywall-mcp never spends. |
| Var | Default | Purpose |
|---|---|---|
PAYWALL_DEFAULT_PRICE_SATS | 0 | Default price for any tool not in the price map. 0 = free passthrough. |
PAYWALL_PRICE_MAP | {} | JSON object mapping tool names to sat prices. Per-tool 0 = free; missing = use default. Example: {"premium_compliment":21,"rare_alpha_signal":5000}. |
| Var | Default | Purpose |
|---|---|---|
PAYWALL_UPSTREAM_CWD | (parent cwd) | Working directory for the upstream child process. |
PAYWALL_UPSTREAM_ENV | (inherits) | JSON object of env-var overrides for the upstream. |
PAYWALL_READ_ONLY | false | Disables all paid tool calls (tools/list still works). Useful for maintenance. |
PAYWALL_INVOICE_TTL_SECONDS | 600 | Invoice TTL. Past this, payment_hash is forgotten from cache and the buyer must re-issue. |
PAYWALL_PRICE_LABEL_TEMPLATE | "(💰 {price} sats)" | Label appended to each priced tool's description in tools/list. {price} is substituted with the sat amount. |
PAYWALL_LOG_PATH | ./paywall-mcp.log | Server log. |
PAYWALL_AUDIT_PATH | ./paywall-mcp-audit.log | NDJSON audit log (one line per call). |
paywall-mcp-test serverThe companion paywall-mcp-test package exposes a single tool — premium_compliment. It already implements its own paywall pattern internally, but it's also a convenient stand-in for "any upstream MCP server" to demonstrate paywall-mcp itself.
.env:
PAYWALL_UPSTREAM_COMMAND=node
PAYWALL_UPSTREAM_ARGS=["/abs/path/to/paywall-mcp-test/dist/index.js"]
NWC_CONNECTION_STRING=nostr+walletconnect://...
PAYWALL_DEFAULT_PRICE_SATS=21
PAYWALL_PRICE_MAP={"premium_compliment":21}
Wire paywall-mcp (not the upstream directly) into your MCP client:
{
"mcpServers": {
"paywall": {
"command": "npx",
"args": ["-y", "paywall-mcp"],
"env": {}
}
}
}
Now from your agent:
1. tools/list → premium_compliment ... (💰 21 sats) This tool requires ...
2. premium_compliment({}) → returns invoice + payment_hash
3. nwc_pay_invoice(invoice) → buyer pays
4. premium_compliment({ payment_hash: "..." }) → upstream's result returned
tools/list → upstream.listTools() → augment descriptions with prices → return
tools/call:
if price == 0 → upstream.callTool(args) (passthrough)
elif PAYWALL_READ_ONLY → refuse with paywall_read_only (block)
elif no payment_hash → gate.issue() → return bolt11 + hash (issue)
elif bad hash format → refuse with invalid_payment_hash (block)
else (have hash):
gate.verify() ──┬─ unknown_payment_hash → block
├─ payment_hash_already_redeemed → block (replay)
├─ payment_hash_tool_mismatch → block
├─ payment_not_settled → block
└─ ok → strip hash → upstream.callTool() (paid passthrough)
Audit log entries (NDJSON, one per request):
outcome: "ok" — invoice issued, free passthrough, or paid passthrough completedoutcome: "blocked" — read-only refusal, invalid hash, replay, mismatch, not-settledoutcome: "error" — upstream call failed, NWC lookup_invoice failed, etc.Tail the audit log for ground truth — independent of whatever the LLM tells you.
tail -f paywall-mcp-audit.log | jq .
{
"mcpServers": {
"paywall": {
"command": "npx",
"args": ["-y", "paywall-mcp"],
"env": {}
}
}
}
Same .env-via-binary-dir pattern as the rest of the substrate — leave env empty in the client config; secrets stay in paywall-mcp/.env.
pnpm typecheck
pnpm test # 13 vitest cases (config resolution + payment-gate state machine)
pnpm build # ~18 KB ESM bundle
nwc-mcp — Lightning wallet for the buyer. Lets the agent pay the invoices paywall-mcp issues. The matching half of the agent-pays-a-paid-tool loop.nostr-ops-mcp — NOSTR identity, publishing, encrypted DMs.marketplace-mcp — Run a NIP-15 / Shopstr storefront from an agent.albyhub-admin-mcp — Alby Hub node-admin via HTTP API.MIT — see LICENSE.
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