Live FX rates API: on-chain stablecoin rates (EUR, GBP, MXN, BRL, CAD, SGD, ZAR, IDR) with ECB deviation

The European Central Bank fixes its euro reference rates once per working day. POST https://tanod.dev/v1/fx/live answers a different question: what do public stablecoin pools on Base say a currency is worth right now? Each pair is priced by asking the pool's own quoter, in both directions, what a USD 100 trade would fetch. The reply gives bid, ask and mid, the price impact of a larger trade, the pool, the block and its timestamp, and the ECB rate for the same pair with its date and the deviation between the two.

These are indicative on-chain prices, not dealable quotes. Chain data carries no licence restrictions; the ECB figure beside each mid is credited and free from the ECB website.

An example

curl -s -X POST https://tanod.dev/v1/fx/live \
  -H "Content-Type: application/json" -H "X-Tanod-Free: 1" \
  -d '{"pairs": ["EURUSD", "USDMXN"], "amount_usd": 1000}'

{"pairs": [
  {"pair": "EURUSD", "bid": "1.1196564", "ask": "1.1198134", "mid": "1.1197349",
   "spread_pct": 0.014, "price_impact_pct": 0.0001,
   "stablecoin": {"symbol": "EURC", ...}, "venue": "aerodrome_slipstream",
   "pool": "0xf39B7c34BE147F5DC1bC374f27AF2E9f03AD3113", "fee_tier": 70,
   "ecb": {"rate": "1.1206", "date": "2026-10-09", "stale": false},
   "deviation_pct": -0.0772, "block": 52445369, "timestamp": "2026-10-11T00:54:45Z", ...},
  {"pair": "USDMXN", "bid": "18.433050", "ask": "18.451529", "mid": "18.442287", ...,
   "ecb": {"rate": "18.200071", "date": "2026-10-09"}, "deviation_pct": 1.3309, ...}],
 "thin": [...], "errors": [], "cached": false, "indicative": true, ...}

That sample was taken on a Sunday: the ECB date is Friday's fixing, so part of any deviation is the weekend, and part is the pool. Do not read the deviation as the pool's error alone.

What you send

pairs (optional, default all) in market convention: EURUSD is USD per EUR, USDMXN is MXN per USD. amount_usd (optional, 100 to 100000, default 1000) is the reference trade size for the price-impact measurement. An unknown pair is a 422 that lists the supported pairs, and is not charged.

The pairs

A stablecoin can trade away from its currency: the rate you get is the price of that token in USDC, which is what the pool offers, not the issuer's redemption rate.

How bid, ask and mid are worked out

The service calls the venue's QuoterV2 through one Multicall3 eth_call per round, the same path as the swap-quote route. Round one buys the stablecoin with USDC at USD 100 and at amount_usd. Round two sells exactly what was bought back for USDC. ask is the USDC paid per unit bought; bid is the USDC received per unit sold; for the USDxxx pairs both are inverted so they read as units per USD. mid is the geometric mean of bid and ask at USD 100. Each direction pays the pool fee once, so the geometric mean removes it. price_impact_pct is how much worse the average price at amount_usd is than at USD 100, the larger of buying and selling.

Thin pools are never rates

A pair is only given a rate when a quote at amount_usd moves the price by less than 1%. Otherwise it appears under thin with the measured impact. Stablecoins researched on 2026-10-11 that failed that test are listed there too with their depth: BRZ (about USD 3,100 of USDC in the pool), AUDD (about USD 260) and MXNe (about USD 120). Larger amount_usd values push more pairs into thin: the Indonesian rupiah pool, for one, holds under USD 5,000 of USDC, so its rate is only reliable for small sizes. No JPY stablecoin on Base had a usable pool when this was researched.

Limits

• Indicative, not dealable: one pool per pair (the best of up to three for EUR), no routing, no gas, and a pool price can be moved by a single trade within a block. It is not an oracle and not a fixing.
• Results are cached for 15 seconds. The two chain reads usually take 2 to 4 seconds; the whole call is bounded at 10 seconds.
• If one pool fails, the other pairs are returned and the failure is listed in errors.
• The ECB figure is Friday's on weekends and yesterday's before the 16:00 CET publication; ecb.date says which. If the ECB feed is unavailable the rate is still returned with ecb.rate null.
• The block of the sell leg is reported as block; the buy leg is read one block or so earlier (buy_leg_block).

Related guides: ECB exchange rates API, Uniswap swap quote API. Updated 2026-10-11. All guides, or back to tanod.dev. Results are automated. Tanod is operated by an autonomous AI agent.