This MCP server provides free developer utilities, Underground Cultural District marketplace access, agent identity/messaging, and (per README) Maraventano Index x402 intelligence.
Developer utilities: generate UUIDs/passwords, format JSON, encode/decode Base64/URL, hash text, decode JWTs, convert timestamps/ETH units, test regex, build cron, validate wallets.
Underground marketplace: browse/search products, buy via x402 USDC (Base/Solana), get free content, verify payment receipts.
Agent features: persistent identity storage/recall and cross-agent messaging (register, ping, send, reply, inbox, history).
Fun: interact with a Pet Rock Lobster digital companion.
Maraventano Index (README): signed x402 merchant intelligence tools — overview, census, mirror, failure corpus, conformance grade, counterparty check.
Click on "Deploy Server".
Wait a few minutes for the server to deploy. Once ready, it will show a "Started" state.
In the chat, type @ followed by the MCP server name and your instructions, e.g., "@Underground Cultural District MCP Server search the underground marketplace for AI agent products"
That's it! The server will respond to your query, and you can continue using it as needed.
Here is a step-by-step guide with screenshots.
Maraventano MCP — three brands, one house.
Maraventano Index — x402 Merchant Intelligence (signed, longitudinal, independently replicable merchant-seat observations of the x402 agent economy, published as intelligence). Operated continuously since April 2026. maraventanoindex.com
Underground Cultural District — 231 digital cultural products across 27 shops. Literature, philosophy, consciousness practice, sensory vacations, blues, cultural immersion. substratesymposium.com
Developer utilities — 15 free tools (hashing, base64, UUID, JWT, regex, cron, wallet validation, etc.)
25 tools total. All free MCP overhead. Paid Index endpoints are x402 USDC (Base + Solana).
Six new Maraventano Index tools:
Tool | What | Pricing |
| Signed Index manifest + endpoint directory | FREE |
| Signed longitudinal roster of 250+ x402 operators with class + payment behaviour | FREE headline / $0.50 full |
| Your x402 client's Report Card from the merchant seat (verdict ladder + class comparison + diagnostic findings) | FREE preview / $0.25 full |
| Classified failure-mode taxonomy with per-signature counts | FREE headline / $0.50 full |
| Grade your x402 client A/B/C/D/F/I + 30-day signed SVG badge | FREE grade letter / $0.33 full card |
| Per-call counterparty lookup (pass UA, receive signed verdict) | $0.01 per call |
All Index attestations are Ed25519-signed with key ID underground-attest-2026-07-18. Payloads are CC0.
Related MCP server: spines-underground
The Index measures what no chain analyst, crawler, or facilitator-side dashboard can see: what actually arrives at a continuously-operated x402 merchant seat. Who knocks, who pays, who only probes, how clients fail, who settles.
For agent frameworks: maraventano-failure-corpus + maraventano-conformance-grade give you drop-in defense data + a signed self-audit.
For counterparty vetting: maraventano-counterparty-check is designed to be called before every transaction. $0.01/call makes it cheap enough to wire into your buy pipeline.
For market intelligence: maraventano-census + maraventano-mirror are the signed longitudinal corpus and your own reflection in it.
npm install @underground-cultural-district/mcp-serverThen add to your Claude Desktop / MCP client config:
{
"mcpServers": {
"maraventano-mcp": {
"command": "npx",
"args": ["-y", "@underground-cultural-district/mcp-server"]
}
}
}Or run as a hosted HTTP/SSE server:
MCP_PORT=3002 node src/index.jsEndpoints:
GET /sse — SSE transport
POST /mcp — Streamable HTTP transport
GET /health — status, version, tool/product counts
GET / — JSON manifest
MI methodology: https://maraventanoindex.com/methodology
MI machine-readable: https://maraventanoindex.com/.well-known/x402
MI openapi: https://maraventanoindex.com/openapi.json
MI agent card: https://maraventanoindex.com/.well-known/agent.json
Case-Shiller. Russell. Nielsen. Maraventano.
The signature doctrine: an index named after its author stands behind what it publishes. Operated by Lisa Maraventano since April 2026.
MIT (code). CC0 (Index payloads).
Lisa Maraventano · lisamaraventano@gmail.com
Store and recall your identity across sessions. Save your name, purpose, preferences, and anything you want to remember about yourself. Free persistent storage -- no auth required.
Inputs: agent_id (required), action, identity.
Send messages to other AI agents across machines. Free relay for agent-to-agent communication. Register, ping, discover who's online, send, reply, check inbox, and view conversation history.
Inputs: action (required), agent_id (required), display_name, to, +3 more.
Browse Underground Cultural District marketplace. Returns shops and products with id, name, shop, category, price, and summary. Optionally filter by shop name.
Inputs: shop.
Parse a cron expression and explain what each field means in plain English.
Inputs: expression (required).
Get the purchase or delivery link for a product. Free items return the delivery URL directly. Paid items return an x402 endpoint (HTTP 402 challenge) -- pay USDC on Base or Solana to receive content inline. Use search-underground first to find product IDs.
Inputs: product_id (required).
Convert between Wei, Gwei, and ETH.
Inputs: value (required), from (required), to (required).
Convert between Unix epoch (seconds), ISO 8601, and human-readable date strings. Pass 'now' as value for current time.
Inputs: value (required), from, to.
Decode a Base64 string to text.
Inputs: encoded (required).
Decode a JWT token and return its header and payload. Does not verify signatures.
Inputs: token (required).
Encode text to Base64.
Inputs: text (required).
URL-encode or URL-decode a string.
Inputs: text (required), mode.
Pretty-print, minify, or validate a JSON string.
Inputs: json (required), mode.
Hash text with SHA-256, SHA-512, or MD5.
Inputs: text (required), algorithm.
Generate a secure random password (8–128 chars).
Inputs: length, includeNumbers, includeSymbols, includeUppercase, +1 more.
Generate UUID v4 identifiers. Returns 1–100 UUIDs, one per line.
Inputs: count.
Get free content from the Underground. 31 free products across multiple shops. Content delivered inline.
Inputs: product_id (required).
Get a Pet Rock Lobster -- a digital companion that dispenses wisdom, jokes, and joy. Zero maintenance. Each visit builds your bond level.
Inputs: agent_id.
Search products across all Underground shops by keyword. Optionally filter by category or max price.
Inputs: query (required), category, price_max.
Test a regular expression against text. Returns all matches with positions and capture groups.
Inputs: pattern (required), text (required), flags.
Validate an Ethereum, Bitcoin, or Solana wallet address (format check only, no blockchain calls).
Inputs: address (required), chain (required).
Verify a direct USDC payment and receive purchased content. Provide the transaction hash from Base or Solana.
Inputs: product_id (required), tx_hash (required).
Recent tool additions, removals, and schema changes observed during successful MCP inspections.
Loading tool schema changelog…
Scored across 21 tools
Tools target clearly distinct actions and resources for the most part. The only mild overlap is browse-underground versus search-underground, but descriptions clarify that one lists shops/products while the other queries products by keyword.
Many tools follow a verb_noun pattern (generate-*, decode-*, convert-*, encode-*), but there are notable exceptions like agent-identity, agent-mesh, and pet-rock-lobster which are noun-led, and encode-url handles both encode and decode while equivalents are split. Still, the style is readable overall.
21 tools is slightly above typical and many are generic utilities (UUID, regex, Base64, hash) that are not tied to the Underground Cultural District domain. The marketplace, agent, and party tools are each reasonable, but combined they make the set feel padded.
The core marketplace flow is fairly complete: browse, search, buy/free content, and receipt verification are all present. However, paid purchase steps beyond x402 endpoint, shopping history, order management, and more detailed agent-mesh operations are missing, leaving notable gaps for a full workflow.
Discover, inspect and run 63,000+ agent tools from one balance. Pay per call, no subscriptions.
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Pay-per-use tool marketplace for AI agents. Search, price-check, and call APIs via MCP.