{ "id": "m4-swap-metamask", "title": "The MetaMask Swap", "extends": "m1-send-metamask", "context": { "wallet": "MetaMask extension", "platform": "Chrome extension", "network": "mainnet", "settings": "defaults", "version": "web/5.157.3", "observed": "2026-08-24", "captures": [ { "run": "20260824-222054-swap-metamask", "tx": "0x407247a9e2133843416136d9c42c6537ee174dc36a2283e71fed3cf4acc4196f" } ] }, "_comment": "MetaMask's BUILT-IN Swap (not a dapp) — the swap most people actually do: in-wallet, no site connect. It extends the M1 send backbone (Infura, feature flags, prices, screening, broadcast). What the swap ADDS is one closed engine: bridge.api.cx.metamask.io/getQuoteStream computes the route, the minimum-out, AND the swap calldata you sign, in one call — the same one-company-computes-what-you-sign risk as U1, but the company is MetaMask itself. Two defaults observed live (run 20260824-214902): the receive token pre-fills to mUSD, MetaMask's OWN stablecoin, and the quote screen discloses a 0.875% MetaMask fee taken on top of network + slippage. The swap executes as a contract call to MetaMask's swap router (MetaSwap; the 'recipient' is that contract, not a person). REAL mainnet tx 0x407247a9…4196f (to MetaSwap, method swap, 0.002 ETH → mUSD), broadcast through MetaMask's Smart Transactions relay. FINDING (run 20260824-222054): the signed swap does NOT go to the public mempool — it is handed to MetaMask's private STX relay (transaction.api.cx.metamask.io/submitTransactions → 200, then batchStatus polling) which lands it via a private/MEV-protected path. It mined, but only after a delay (>2 min past submit), and it was never publicly visible in flight: a closed relay sits between you and inclusion, and while you wait you can only see the relay's own status, not the chain's.", "prepend_steps": [ { "id": "swap-tokens", "phase": "discover", "name": "Token list · what you can swap", "host": "tokens.api.cx.metamask.io/v3/assets", "actor": "consensys-apis", "purpose": "The swappable-token list the Swap screen offers, with each token's price and metadata", "need": "R", "carries": [ "ip", "selected_address" ], "returns": "which tokens you can pick, and the mUSD default it fills", "can_block": true, "on_failure": "degrade", "worst_lie": { "outcome": "false_belief", "note": "the list decides what you can swap into and what it's labelled; the receive field defaults to MetaMask's own mUSD" }, "removable_by": "none", "provenance": { "status": "observed", "ref": "20260824-214902-swap-metamask · tokens.api.cx.metamask.io /v3/assets, token.api.cx.metamask.io" }, "notes": "The receive token pre-fills to mUSD (MetaMask's own stablecoin) — a self-default the user did not choose.", "fixed_by": [ "local-indexing" ] }, { "id": "swap-quote", "phase": "discover", "name": "MetaMask swap engine · route + calldata + fee", "host": "bridge.api.cx.metamask.io/getQuoteStream", "actor": "consensys-apis", "purpose": "One streamed call returns the route, the minimum received, the 0.875% MetaMask fee, and the swap-router calldata the wallet will sign", "need": "RC", "carries": [ "ip", "selected_address", "token_pair", "amount", "holdings" ], "births": [ "unsigned_tx", "swap_route" ], "returns": "the price you act on and the exact bytes you sign", "can_block": true, "on_failure": "blocks", "failure_note": "no quote → no swap; there is no second quote source in the UI", "worst_lie": { "outcome": "funds_lost", "note": "one closed API sets the route, the minimum-out, and the calldata together — a bad minOut drains you within slippage and the wallet can't check the custom-encoded calldata locally" }, "removable_by": "none", "tx_input": "field", "provenance": { "status": "observed", "ref": "20260824-214902-swap-metamask · GET bridge.api.cx.metamask.io/getQuoteStream" }, "notes": "MetaMask merged Swaps + Bridge into one 'bridge' quote API. The quote screen discloses 'Includes 0.875% MetaMask fee' on top of network fee and 2% default slippage.", "fixed_by": [ "verifiable-rpc", "indie-frontends" ] } ], "own_node": { "node": "192.168.68.54", "runs": [ "20260924-213710-swap-metamask-localnode" ], "steps": { "swap-tokens": { "state": "out", "ref": "tokens.api.cx.metamask.io · 1 req after switch" }, "swap-quote": { "state": "out", "ref": "bridge.api.cx.metamask.io · 2 req after switch · /getquotestream" }, "ext-update": { "state": "unseen", "ref": "clients2.google.com seen before the switch only, not after" }, "feature-flags": { "state": "out", "ref": "client-config.api.cx.metamask.io · 1 req after switch" }, "phishing-list": { "state": "unseen", "ref": "phishing-detection.api.cx.metamask.io seen before the switch only, not after" }, "c2-list": { "state": "unseen", "ref": "client-side-detection.api.cx.metamask.io seen before the switch only, not after" }, "token-list": { "state": "out", "ref": "token.api.cx.metamask.io · 2 req after switch" }, "spot-prices": { "state": "out", "ref": "price.api.cx.metamask.io · 5 req after switch · /v3/spot-prices" }, "fiat-rates": { "state": "unseen", "ref": "price.api.cx.metamask.io still contacted (5 req) but this exact call wasn't singled out" }, "accounts-balances": { "state": "out", "ref": "accounts.api.cx.metamask.io · 3 req after switch · /v4/multiaccount/balances" }, "balance-fallback": { "state": "local", "ref": "192.168.68.54 · eth_call; mainnet.infura.io got 0 after switch" }, "nft-detection": { "state": "unseen", "ref": "nft.api.cx.metamask.io seen before the switch only, not after" }, "defi-positions": { "state": "unseen", "ref": "defiadapters.api.cx.metamask.io seen before the switch only, not after" }, "icons": { "state": "out", "ref": "static.cx.metamask.io · 1 req after switch" }, "block-poll": { "state": "local", "ref": "192.168.68.54 · eth_blockNumber; mainnet.infura.io got 0 after switch" }, "segment": { "state": "out", "ref": "api.segment.io · 4 req after switch" }, "sentry": { "state": "out", "ref": "sentry.io · 15 req after switch" }, "screen-recipient": { "state": "unseen", "ref": "not in these runs" }, "nonce": { "state": "unseen", "ref": "mainnet.infura.io seen before the switch only, not after" }, "gas-fees": { "state": "out", "ref": "gas.api.cx.metamask.io · 2 req after switch · suggestedgasfees" }, "estimate-gas": { "state": "unseen", "ref": "mainnet.infura.io seen before the switch only, not after" }, "simulation": { "state": "out", "ref": "tx-sentinel-ethereum-mainnet.api.cx.metamask.io · 2 req after switch" }, "security-alert": { "state": "unseen", "ref": "not in these runs" }, "stx-broadcast": { "state": "unseen", "ref": "not in these runs" }, "inclusion": { "state": "unseen", "ref": "not in these runs" }, "stx-status": { "state": "unseen", "ref": "not in these runs" }, "receipt-poll": { "state": "unseen", "ref": "mainnet.infura.io seen before the switch only, not after" }, "etherscan-check": { "state": "unseen", "ref": "not in these runs" }, "balance-refresh": { "state": "unseen", "ref": "accounts.api.cx.metamask.io still contacted (3 req) but this exact call wasn't singled out" } }, "unmapped": [ "tron-mainnet.infura.io", "solana-mainnet.infura.io", "bitcoin-mainnet.infura.io", "user-storage.api.cx.metamask.io", "monad-mainnet.infura.io", "subscription.api.cx.metamask.io", "base-mainnet.infura.io", "bsc-mainnet.infura.io", "carrot.megaeth.com", "api.merkl.xyz", "optimism-mainnet.infura.io", "polygon-mainnet.infura.io", "testnet-rpc.monad.xyz", "arbitrum-mainnet.infura.io", "linea-mainnet.infura.io", "linea-sepolia.infura.io", "sepolia.infura.io", "notification.api.cx.metamask.io", "geolocation.api.cx.metamask.io", "on-ramp-cache.api.cx.metamask.io", "authentication.api.cx.metamask.io", "metamask.github.io", "gateway.api.cx.metamask.io", "cdn.contentful.com" ] } }