Tandem
View + trade only. Never withdraw.

Let someone trade your Coinbase account — strictly inside your rules.

Tandem connects your Coinbase account with a view-and-trade-only API key, then hands a delegate a trading desk fenced in by the guardrails you set. They can trade or just recommend. They can never move a cent off the exchange.

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Coinbase Advanced Trade API · CDP keys (ES256 / Ed25519) · your keys, your account

Guardrails, not trust falls

Twenty rule kinds — asset whitelists, notional and daily caps, minimum holding periods, price floors, trading windows, drawdown halts. The policy engine runs server-side when a trade is proposed and again when it executes, so a delegate physically cannot step outside your rules.

Agreements as data

Set a benchmark (say, the best of BTC, ETH and 100% over 24 months), add a hurdle and a profit share. Both parties sign the exact terms hash, and Tandem evaluates the numbers every day — no spreadsheets, no arguments.

Analytics vs BTC and ETH

TWR and money-weighted returns, drawdowns, Sharpe / Sortino / Calmar, beta and alpha against BTC and ETH, up/down capture, per-asset attribution and trade statistics — the numbers a broker app will not show you.

The safety comes from the architecture, not a promise

Withdrawal is not a feature Tandem chose to disable. There is no code path for it, and keys that could do it are turned away at the door.

Transfer keys are refused
Onboarding checks the key's permissions. If it can withdraw, Tandem rejects it outright and records why — it is never stored.
Keys are sealed, not stored
Every key gets its own AES-256-GCM data key, wrapped by a root key that lives only in the server environment.
Append-only audit
Each entry is hash-chained to the one before it, so the trail can be verified and cannot be quietly rewritten.

Four steps

  1. 01ConnectPaste a Coinbase CDP key with view and trade scopes. Tandem verifies the permissions and refuses anything that can transfer.
  2. 02ShareInvite a delegate by email and choose what they can do: recommend only, or trade — with an approval threshold if you want one.
  3. 03Set the rulesAdd guardrails from the catalogue. Every proposal is checked against all of them, and the delegate sees exactly which one blocked it.
  4. 04TrackWatch performance against BTC, ETH and your agreement's hurdle, with fee accrual computed the same way for both parties.