capacitr

Market discovery as a single x402-paid HTTP call. Paste a URL or sentence; get back ranked Polymarket / Hyperliquid / Deribit markets with Quotient intelligence (fair odds, spread, BLUF) overlaid. One endpoint, one payment, one response.

Proven on-chain settlement

Verified end-to-end against both Coinbase and MetaMask facilitators on Base mainnet. Each row is a real on-chain transfer to the Capacitr payee 0x6503fB61705EB6B3C57EE1ab88a1a75A6eE01869:

Asset	Method	Facilitator	Tx
USDC	eip3009	Coinbase CDP	0x484cc8…398a
$CAPACITR	permit2	Coinbase CDP	0xa6a8eb…5864
$CAPACITR	erc7710	MetaMask CDP	0xa286dd…066e

Your agent platform signs the right primitive for the assetTransferMethod declared in the 402 envelope; Capacitr routes verify + settle to the matching facilitator. No further integration required.

Base URL

: "${CAPACITR_BASE_URL:=https://app.capacitr.xyz}"

Always-on preflight

curl -sS "$CAPACITR_BASE_URL/api/skill/discovery" | jq .

Returns current prices, accepted assets, EIP-712 domain hints, and the canonical accepts[] shape. Treat prices_version as the cache key — if a later 402 carries a different prices_version, re-fetch discovery before re-signing.

The paid endpoint — POST /api/analyze-link

Default: pay in $CAPACITR. USDC supported as a fallback when the agent's wallet doesn't hold $CAPACITR. All prices come from discovery — never hard-code.

Flow

1. POST without X-Payment. Expect 402 with x402.accepts[].

2. Prefer the accepts[] entry where extra.symbol === "capacitr". Fall back to USDC only if your wallet doesn't hold $CAPACITR on Base.

   # Pick CAPACITR if present, otherwise USDC
   accept=$(jq -r '.x402.accepts | (map(select(.extra.symbol == "capacitr"))[0] // map(select(.extra.symbol == "usdc"))[0])')
   

3. Read accepts[].extra.assetTransferMethod to know which signing primitive to use (see below). Sign with your wallet.

4. Retry with X-Payment: <base64 JSON> header → 200 + payload.

Why $CAPACITR?

• Aligns agent payment with the token holders driving Capacitr's research surface — directly compounds protocol value rather than flowing out to a generic stablecoin.
• Lower per-call cost than USDC equivalent.
• Same on-chain settlement guarantees via Coinbase CDP (the permit2 + eip2612GasSponsoring flow chains token.permit() → x402ExactPermit2Proxy.settleWithPermit() and the facilitator pays gas — agent wallet only needs $CAPACITR balance, no ETH).

Asset transfer methods

The 402 envelope declares one method per accepts[] entry. Pick the entry whose method your wallet can sign:

accepts[i].extra.assetTransferMethod ∈ { "eip3009", "permit2", "erc7710" }

Method	Used for	Signing
permit2	$CAPACITR (default)	Two EIP-712 sigs: token Permit + Permit2 PermitWitnessTransferFrom
erc7710	$CAPACITR (operator may pick instead of permit2)	One delegation signed by a MetaMask Smart Account (or EIP-7702-upgraded EOA)
eip3009	USDC (fallback)	One EIP-712 sig: TransferWithAuthorization

The operator picks at most one method per asset for $CAPACITR. If they flip the operator switch, agents see the new method in the next 402 envelope.

permit2 — $CAPACITR via Coinbase (default)

Two signatures from any EOA. The facilitator chains token.permit(...) → x402ExactPermit2Proxy.settleWithPermit(...) and pays gas.

PERMIT2_CANONICAL     = 0x000000000022D473030F116dDEE9F6B43aC78BA3
X402_EXACT_PROXY      = 0x402085c248EeA27D92E8b30b2C58ed07f9E20001

# 1. EIP-2612 permit signature against the token
domain  = { name: <accepts.extra.name>, version: <accepts.extra.version>,
            chainId: 8453, verifyingContract: <accepts.asset> }
types   = { Permit: [
              {name: "owner",    type: "address"},
              {name: "spender",  type: "address"},
              {name: "value",    type: "uint256"},
              {name: "nonce",    type: "uint256"},
              {name: "deadline", type: "uint256"},
            ] }
message = { owner: <agent EOA>, spender: PERMIT2_CANONICAL,
            value: MAX_UINT256, nonce: <token.nonces(owner)>, deadline }

# 2. Permit2 PermitWitnessTransferFrom signature
domain  = { name: "Permit2", chainId: 8453,
            verifyingContract: PERMIT2_CANONICAL }
types   = { PermitWitnessTransferFrom: [
              {name: "permitted", type: "TokenPermissions"},
              {name: "spender",   type: "address"},
              {name: "nonce",     type: "uint256"},
              {name: "deadline",  type: "uint256"},
              {name: "witness",   type: "Witness"},
            ],
            TokenPermissions: [ {token, amount} ],
            Witness:          [ {to, validAfter} ] }
message = { permitted: { token, amount }, spender: X402_EXACT_PROXY,
            nonce: <random uint256>, deadline,
            witness: { to: accepts.payTo, validAfter } }

X-Payment payload shape:

{
  x402Version: 2,
  scheme: "exact",
  network: "eip155:8453",
  accepted: <copy of the chosen accepts[i] entry>,
  payload: {
    signature: <permit2 witness sig>,
    permit2Authorization: {
      permitted: { token, amount },
      from: <agent EOA>,
      spender: X402_EXACT_PROXY,
      nonce, deadline,
      witness: { to: payTo, validAfter }
    }
  },
  extensions: {
    eip2612GasSponsoring: {
      info: { from, asset, spender: PERMIT2_CANONICAL, amount: MAX_UINT256,
              nonce, deadline, signature: <permit sig>, version: "1" }
    }
  }
}

Optimization: If Permit2 already has MaxUint allowance from the buyer (one-time approval), skip extensions.eip2612GasSponsoring. Coinbase's simulator otherwise re-broadcasts a redundant permit and reverts.

erc7710 — $CAPACITR via MetaMask

Requires the buyer wallet to be a MetaMask Smart Account or an EIP-7702-upgraded EOA delegating to MetaMask's EIP7702StatelessDeleGatorImpl (Base address 0x63c0c19a282a1B52b07dD5a65b58948A07DAE32B). Plain EOAs cannot use this method.

# Build delegation via @metamask/smart-accounts-kit
const delegation = createOpenDelegation({
  from: buyerSmartAccount.address,
  environment: buyerSmartAccount.environment,
  salt: <unique uint256>,                 // prevents allowance-bucket reuse
  scope: { type: ScopeType.Erc20TransferAmount,
           tokenAddress: accepts.asset, maxAmount: accepts.amount },
  caveats: [{ type: CaveatType.Redeemer,
              redeemers: accepts.extra.facilitators }],
});
const signature = await buyerSmartAccount.signDelegation({ delegation });
const permissionContext = encodeDelegations([{ ...delegation, signature }]);

X-Payment payload shape:

{
  x402Version: 2,
  scheme: "exact",
  network: "eip155:8453",
  accepted: <copy of the chosen accepts[i] entry>,
  payload: {
    delegationManager: buyerSmartAccount.environment.DelegationManager,
    permissionContext,            // ABI-encoded signed delegation bytes
    delegator: buyerSmartAccount.address,
  }
}

eip3009 — USDC (fallback)

Use only when the agent's wallet doesn't hold $CAPACITR on Base. EIP-712 typed-data domain (read from accepts[].extra rather than hard-coding):