PayPerByte MCP Server

A Model Context Protocol server that gives AI agents direct access to PayPerByte — cryptographically attested, provenance-verifiable data feeds for AI agents (the X-BYTE-Attestation receipt proves delivery-integrity — these are exactly the bytes PayPerByte served and attested under the BYTE Library domain — not that an independent data publisher signed them, and not that the data is correct). Agents discover feeds, pay-per-call via x402 (settled in USDC on Base mainnet), or subscribe to on-chain streams (Arbitrum Sepolia testnet). Every paid x402 response carries an EIP-712 PayloadAttestation receipt (X-BYTE-Attestation header) the agent verifies before acting. No tokens, no API keys, no off-chain accounts.

Two rails — read this before setting PRIVATE_KEY.

• x402 pay-per-call (byte_buy_data): Base mainnet (eip155:8453), REAL USDC. Paid feeds settle real money — every price is quoted in the 402 challenge and listed per feed at https://x402.payperbyte.io/feeds. Example: the Merchant Screen Oracle returns a signed ALLOW/WARN/BLOCK check on a merchant's domain and payout address, backed by a signed EIP-712 attestation over the exact response bytes, run before an agent settles an x402 payment to it. Authenticity and delivery-integrity, not a correctness guarantee on the verdict itself — and on the domain, address and price you supply; it does not observe or constrain the address you ultimately settle to. Use a dedicated wallet holding only what you intend to spend.
• On-chain subscribe/publish/query layer (BYTE Library contracts + indexer): Arbitrum Sepolia testnet (chain 421614), MockUSDC. Mainnet for this layer is gated on an external security audit. The EIP-712 attestation signing domain stays anchored at 421614 regardless of which rail you paid on.

One PRIVATE_KEY serves both rails. Never reuse a key holding funds you can't afford to spend.

Quick start

npx -y byte-mcp-server

Wire it into your MCP client (Claude Desktop config below), then your agent can:

• Discover feeds: "List the PayPerByte catalog" / "Search publishers for weather"
• Screen a counterparty before you pay it (x402, no setup): "Screen this domain and payout address before I settle" → real USDC on Base mainnet at the price the 402 challenge quotes, signed ALLOW/WARN/BLOCK verdict from the Merchant Screen Oracle with an attestation receipt
• Try it cheap first: "Get the weather" / "Any earthquakes over M4 today?" → real USDC at each feed's listed price (https://x402.payperbyte.io/feeds), same attestation receipt on every response — the cheapest way to see verify-before-act work before spending on a verdict
• Subscribe to a stream (testnet): "Subscribe me to the earthquakes feed" → auto-approves MockUSDC for ongoing settlement on Arbitrum Sepolia
• Query a fact-oracle (testnet): post a signed EIP-712 question to a registered fact-oracle publisher for an on-chain signed answer with citations — when a fact-oracle publisher is live (none is broadcasting today; the tool times out until one registers and broadcasts)

The live catalog is at x402.payperbyte.io/feeds — cryptographically attested, provenance-verifiable feeds across weather, markets, code, security, and knowledge.

Verify before acting (ForeSeal)

See the whole verify-before-act loop in one command — no install, no signup, no wallet:

npx @foreseal/demo

It runs locally (no real USDC) and shows an agent ACT on genuine bytes and REFUSE four attacks — a tampered byte, a forged signature, a missing receipt, a forked signing domain — in about a second.

The same primitive ships as two packages you can drop into your own stack:

• Kit — @payperbyte/sdk: the buyer verifies a receipt before acting.
• Gate — @foreseal/gate: a seller stamps a verifiable receipt on any x402 endpoint.

Two paradigms: subscribe vs. buy

| Mode | Tool | Rail | Best for | Pricing | |---|---|---|---|---| | Buy (x402) | byte_buy_data | Base mainnet — real USDC | One-off needs (single snapshot or verdict for this user query) | Per-feed, quoted in the 402 challenge; live list with prices: https://x402.payperbyte.io/feeds | | Subscribe | byte_subscribe | Arbitrum Sepolia — testnet MockUSDC | Continuous streams (every weather update, every new earthquake) | $0.003 / KB per delivery |

Buy is zero-setup, pay-as-you-go, and live with real settlement; subscribe delivers every broadcast on the audit-gated testnet layer. Pick by access pattern.

Buying a verdict (POST oracle)

GET data feeds need only a feed. Any feed whose method includes POST (live list: https://x402.payperbyte.io/feeds) takes the query as a body — byte_buy_data switches the call from GET to POST automatically. The verdict oracles — feeds that return a signed ALLOW/WARN/BLOCK — are merchant-screen, address-reputation, sanctions-screen, pkg-verdict, reasoning-verdict:

// byte_buy_data tool call — screen a merchant/counterparty before settling
{
  "feed": "merchant-screen",
  "body": { "domain": "example.com", "address": "0x1234…abcd", "observed_price_atomic": "100000" }
}

The paid response returns the signed verdict and an inline verify-before-act result over the X-BYTE-Attestation receipt:

{
  "feed": "merchant-screen",
  "paid": true,
  "price": "$0.100000",   // illustrative — the amount the 402 challenge quoted at buy time
  "txHash": "0x…",
  "data": { "answer": { "verdict": "ALLOW", "reasons": ["…"] }, "attestation": { "…": "…" } },
  "verification": { "verified": true, "hashMatch": true, "signerMatch": true,
                    "reason": "receipt verified — bytes intact AND signed by the pinned gateway attester (safe to act)" }
}

Act only when verification.verified === true — the receipt proves provenance and integrity, not correctness. Other POST bodies: address-reputation {domain,address}, sanctions-screen {address|name}, pkg-verdict {ecosystem,package[,version]}, reasoning-verdict {subject}. Omit body entirely for GET data feeds (weather, earthquakes, …).

Tools (15 total)

Discovery (read-only, no wallet)

| Tool | Description | |---|---| | byte_search_publishers | Search publishers by topic and sort order | | byte_list_feeds | List the active feed catalog with prices and frequencies | | byte_get_publisher | On-chain info for one publisher (status, subscribers, messages, USDC revenue, schema) | | byte_get_network_stats | Network-wide stats: publishers, messages, total fees settled | | byte_check_subscription | Is subscriber subscribed to publisher? | | byte_list_my_subscriptions | All active subscriptions for a wallet — last 7d/30d messages + USDC spend | | byte_subscription_health | Content-drift signal for a publisher: stable / moderate / significant / unknown | | byte_get_token_balances | USDC + ETH balances on Arbitrum Sepolia | | byte_verify_payload | Verify-before-act. Recompute keccak256 of the bytes your agent received and check them against the publisher's on-chain EIP-712 PayloadAttestation — anchor with an expectedHash you hold or the settlement txHash (which also recovers the signer and confirms it's the named publisher). If verified: false, the data was tampered/corrupted in transit — don't act on it |

Subscribe to a stream (requires PRIVATE_KEY)

| Tool | Description | |---|---| | byte_subscribe | Subscribe to a publisher's stream. Auto-bundles USDC approve(max) unless skipAllowance: true (closes a silent-payment-failure footgun where the contract's allowance-skip path delivered data with amount=0) | | byte_unsubscribe | Unsubscribe — takes effect next block | | byte_register_publisher | Register as a data publisher (schema + on-chain registration). v1 is first-party only; stake = 0 | | byte_publish_data | Publish a payload to a subscriber via DataStream (settles fee in USDC). See migration notice above re: r2 |

Buy on-demand (requires PRIVATE_KEY)

| Tool | Description | |---|---| | byte_buy_data | Buy one packet from any feed via the x402 gateway — real USDC on Base mainnet. No subscription, no allowance. Signs EIP-3009 transferWithAuthorization against the 402 challenge; the facilitator settles on-chain. Returns the data + tx hash inline | | byte_query_fact | Ask a slashable fact-oracle publisher a question. Signed EIP-712 request (binds query to your wallet so leaked queries can't burn your escrow); the answer is broadcast on-chain to your address with citations. Requires a live fact-oracle publisher — none is broadcasting today, so the call times out until one registers. |

Configuration

Claude Desktop

Edit ~/.config/claude/claude_desktop_config.json (Linux) or ~/Library/Application Support/Claude/claude_desktop_config.json (macOS):

{
  "mcpServers": {
    "payperbyte": {
      "command": "npx",
      "args": ["-y", "byte-mcp-server"],
      "env": {
        "PRIVATE_KEY": "0x...",
        "RPC_URL": "https://sepolia-rollup.arbitrum.io/rpc",
        "INDEXER_URL": "http://localhost:8080"
      }
    }
  }
}

PRIVATE_KEY is optional — read-only tools work without it. Add it to enable subscribe, publish, buy, and query.

Claude Code

claude mcp add payperbyte -- npx -y byte-mcp-server

Environment variables

| Variable | Required | Default | Description | |---|---|---|---| | PRIVATE_KEY | only for write/buy/query tools | — | EOA key. Signs real Base-mainnet USDC for byte_buy_data and testnet txs for subscribe/publish/query — use a dedicated wallet | | RPC_URL | no | https://sepolia-rollup.arbitrum.io/rpc | Arbitrum Sepolia RPC (the on-chain read/subscribe layer) | | INDEXER_URL | no | https://feeds.payperbyte.io | PayPerByte indexer API | | BYTE_GATEWAY_URL | no | https://x402.payperbyte.io | x402 gateway base URL (used by byte_buy_data) | | BYTE_GATEWAY_ATTESTER | no | current gateway attester (0xB48CCc9e3ab67041e3b5D09700138E45cda6AeA8, rotated 2026-08-19) | Attester address byte_buy_data pins the delivery receipt against. If the gateway rotates before this package updates, set this to the new receipt.attester from /.well-known/agent.json — a stale pin fail-closes buys AFTER payment settles | | MAX_PAYMENT_USDC | no | — (uncapped) | Server-side spend cap for byte_buy_data, in decimal USDC (e.g. 0.25). When set, any 402 quote above the cap is refused before signing; unset means no cap — a dedicated thin wallet remains the hard backstop |

Network

Two rails, honestly stated:

• x402 payment rail (byte_buy_data): Base mainnet (eip155:8453). Paid feeds settle real USDC through the gateway at x402.payperbyte.io; each paid 200 returns an X-BYTE-Attestation EIP-712 receipt over the exact response bytes.
• On-chain layer (subscriptions, broadcasts, fact-oracle escrow, indexer): Arbitrum Sepolia (chain 421614). Mainnet for the BYTE Library contracts is gated on an external security audit. The EIP-712 PayloadAttestation signing domain is anchored on 421614 regardless of the payment rail.

Contract addresses are pinned in the bundled config; the npm release ships ready-to-use defaults. No token.

Development

git clone https://github.com/0rkz/byte-mcp-server.git
cd byte-mcp-server
npm install
npm run build && npm start

License

MIT — see LICENSE.

Starter kit

Optional paid kit ($39): the buyer-side agent kit — an agent that buys and verifies feeds, with drop-in Claude Desktop / Claude Code / Cursor config and a free 30-minute readiness call included. The npm packages are and stay free MIT — the kit sells the assembled setup.

Links

• payperbyte.io — PayPerByte home
• x402.payperbyte.io/feeds — live feed catalog
• Model Context Protocol — MCP spec
• MCP TypeScript SDK
• gold-402 — curated directory of live x402 services (PayPerByte is listed)