Stellar Trustlines Explained
A trustline is your Stellar account's explicit opt-in to hold a particular issued asset. With one exception — native XLM — you need a trustline before you can receive, hold or trade anything on Stellar. It's a small but important concept that explains a lot about how Stellar assets and markets work.
What is a trustline?
A trustline is a record on your Stellar account that says "I'm willing to hold this asset from this issuer." Until that line exists, your account simply can't receive the asset. Native XLM is the only asset that needs no trustline — everything else (USDC, EURC, AQUA, and so on) requires one to the specific issuer that created it.
Most Stellar wallets add the trustline for you automatically when you choose to add an asset, so in practice it's usually a single confirmation.
Why Stellar requires them
Stellar uses an issuer model: any account can issue an asset, identified by a code plus that issuer's address. Trustlines are what keep this open system usable. They let you decide which issuers you accept, so nobody can force unwanted tokens onto your account, and they tell the network exactly which assets each account can hold and trade.
The base-reserve cost
Each trustline is a small "subentry" on your account, and Stellar requires accounts to hold a minimum XLM balance that scales with their subentries. The base reserve is 0.5 XLM per trustline, locked (not spent) for as long as the trustline is open. Remove the trustline later and that reserve is freed. It's a tiny anti-spam cost that keeps the ledger lean.
Asset code + issuer = a unique asset
This is the part that trips people up: on Stellar an asset is the combination of its code and its issuer, not the code alone. Two tokens called USDC from different issuers are different assets and trade in separate markets — so the issuer always matters when you read a price. (See What is USDC on Stellar? for a concrete example with Circle's issuer.) Chartui shows the issuer next to every pair for exactly this reason.
Trustlines & trading on the DEX
Because trading a pair means holding both of its assets, you'll need a trustline to each non-XLM asset in a market before you can place offers or provide pool liquidity for it. Once your trustlines are set, the whole Stellar DEX — order book, liquidity pools and live market data — is open to you, and Chartui lets you watch all of it in real time.