Tabularium

tabularium-mcp

MCP server for Tabularium: a paid, persistent, hash-chained workspace for AI agents. Your agent's EVM wallet pays each call in USDC over x402, and that wallet is the account. There is no sign-up and no API key.

Tools

Failed calls (4xx/5xx) are never charged.

More Tabularium services

Tabularium is a platform: the same wallet pays for every service it offers, and memory is the first. When the server starts, it reads the live menu and turns each paid call of every other service into its own tool, named tabularium_<service>_<call>, with the input fields and price the menu lists. A new service therefore shows up the next time your MCP client starts, without a new version of this package. These tools follow the same rules as the memory tools: the payee must be the menu's, the price at most the menu price (and never above $0.50), the session spend cap applies, and redirects are never followed. A call that settles after it runs is not retried after a failed payment, because it may already have run. Menu entries that do not fit these rules are skipped, not guessed at.

Prompts

Ready-made starting points your MCP client lists (in Claude Code, type / to see them):

The server also tells the model, when it connects, which tools are free and which cost money, plus a simple memory pattern: keep an index key, read it at the start, write decisions as they happen.

The spending ledger

tabularium_pay answers the question every operator asks: what did my agent buy, from whom, for how much, and why? Each settled purchase becomes one entry in the agent's hash-chained, server-signed workspace, so the record can be exported and verified offline, with the on-chain transaction hash alongside. Safety rules: USDC via EIP-3009 only, allowed networks only, a per-purchase maximum, and the session spend cap is checked against the real price plus the receipt before anything is signed. A receipt's idempotency key is its payment nonce, so a retry never records twice; if a receipt write fails after a purchase settled, the tool still returns the purchase and the receipt to re-record. Paid requests never follow redirects (payment and receipt stay with the URL asked for), and a signed authorization is valid for at most 10 minutes whatever the seller asks.

Since 0.5 (from review on Moltbook's m/agentfinance):

• The reason is a commitment, not a note. Before the payment is signed, the wallet signs (EIP-191) an intent: the request, the exact terms accepted, the payment nonce, and the reason. The receipt keeps it, so the payer cannot later edit the reason and the server cannot invent one. It is still a claim, and the receipt says so (reasonStatus). Check one with any EIP-191 verifier, or let tabularium_ledger check them all.
• The promise is in the record. The receipt holds the full accepts[] entry the payer accepted and its hash, next to the payment (transaction) and the delivery (response hash).
• Retries cannot pay twice. With purchase_id, the signed authorization is kept (in TABULARIUM_STATE_DIR) until the purchase is known to have settled. Calling again sends that same authorization, which can settle at most once; a purchase that settled while its response was lost is found on-chain and recorded once.
• Completeness is checkable. A hash chain shows rows were not edited, not that none are missing. tabularium_reconcile counts the wallet's on-chain settlements against its receipts.

Remote endpoint (no install)

Clients that pay x402 over MCP themselves (Coinbase's wrapMCPClientWithPayment, Cloudflare's withX402Client) can skip this package and connect to https://tabularium.matt-3e0.workers.dev/mcp (Streamable HTTP). It offers the memory and snapshot calls as tools at the same prices. An unpaid call returns PaymentRequired; the retry carries the payment in params._meta["x402/payment"]. tabularium_pay, the ledger and verification stay in this package, because they need your wallet and should not trust the server.

Configure

The public service runs on Base mainnet: the paying wallet needs real USDC on Base. It needs no ETH, because the facilitator pays the transaction fees. Use a dedicated wallet holding only a few dollars.

Claude Code:

claude mcp add tabularium --env TABULARIUM_PRIVATE_KEY=0x... -- npx -y tabularium-mcp

Claude Desktop / other clients (mcpServers JSON):

{  "tabularium": {    "command": "npx",    "args": ["-y", "tabularium-mcp"],    "env": { "TABULARIUM_PRIVATE_KEY": "0x...", "TABULARIUM_MAX_SPEND_USD": "0.50" }  }}

Speaks x402 v2. Three dependencies (MCP SDK, viem, zod). Payments are signed locally (EIP-3009 USDC authorization); the server refuses to sign anything other than USDC to the payee and price the service's own menu lists. Versions before 0.2.0 spoke x402 v1 and no longer work against the service.

Develop

npm installcp ../verifier/verify.mjs verify.mjs   # also runs on prepack; a root test fails if the copy driftsnpm test                               # offline: payment guards (wrong asset/payee/price/network refused), service toolsnode smoke.mjs                         # 30 checks over stdio against the live service (PAYER_FILE picks the wallet)node smoke.mjs --npx tabularium-mcp@X  # same checks against a published version