The first time you trade a particular token on an EVM DEX, you'll be asked to confirm twice: once to 'approve', then again to swap. This surprises almost everyone. Here's what's really happening — and why it matters for your security later.
What an approval is
On EVM chains tokens follow the ERC-20 standard, and a token contract won't let another contract move your balance unless you've granted permission. That permission is the approval: a separate on-chain transaction telling the token, "this DEX contract may spend up to X of my balance." Only then can the swap itself run.
Why it's a separate, paid step
- It's a real on-chain transaction, so it carries its own small gas fee.
- It's usually a one-time step per token per spender — your next swap of that token on the same DEX skips it.
- Solana uses a different model, so you typically won't see a separate approve step there.
Unlimited vs. exact approvals
Many DEXes default to an unlimited approval so you never approve that token again. Convenient — but it means the contract can move any amount of that token, indefinitely, until you revoke it. A more cautious option, offered by some interfaces, approves only the exact amount you're about to trade.
| Unlimited approval | Exact approval | |
|---|---|---|
| Convenience | Approve once, never again | Re-approve each trade |
| Extra gas | None after the first | A small fee each time |
| Risk if contract is hacked | Whole balance exposed | Only the approved amount |
For trusted, established DEXes, unlimited is common and usually fine. For new or unaudited contracts, exact approvals are the safer habit.
Why this matters later
Approvals are also how many wallet-draining scams work: a malicious site tricks you into approving its contract, then sweeps the token. That's why managing and revoking approvals is its own security lesson — review the permissions you've granted from time to time.
- Granting unlimited approvals to brand-new, unaudited contracts without a thought.
- Never reviewing or revoking old approvals, leaving stale permissions open for years.
- Assuming the approval moved your tokens. It only grants permission; the swap is the next step.