What it is
Most automated market makers (AMMs) require liquidity providers to deposit two tokens in a fixed ratio (like ETH and USDC together). Single-sided liquidity lets a liquidity provider (LP) or a project deposit only one token, while the protocol's pricing logic — not a matched counterparty — handles the other side of every trade. A trader can swap against that one-sided pool as if a full pair existed.
How it works
- An LP deposits a single token (say, a new project's token) into a pool, with no need to pair it against a second asset.
- The protocol uses an internal price oracle or an algorithmic curve to determine what the token is "worth" against a reference asset (often a stablecoin or ETH) at any moment.
- When a trader wants to buy the token with the reference asset, the contract mints or releases token supply from the pool at the computed price, adjusting the curve as inventory changes.
- The protocol tracks its own inventory of the deposited token versus a synthetic or virtual balance of the reference asset — it doesn't need real reference-asset liquidity sitting idle.
- Fees accrue to the pool from each trade, and impermanent loss is reshaped: instead of losing relative to holding both assets, the LP's exposure shifts entirely based on the single token's price movement and the curve's own risk parameters.
- Some designs (proactive market making, PMM) let the curve flatten near the oracle price to reduce slippage, then steepen as inventory is depleted, mimicking order-book depth with one-sided capital.
Why designers use it
- Lets a token launch with deep liquidity without first sourcing a paired asset, lowering the capital bar for new projects.
- Reduces idle capital: LPs don't need to hold two assets they may not want simultaneously.
- Can produce tighter spreads near the market price than constant-product pools, since it leans on an oracle instead of pure ratio math.
- Simplifies LP UX — deposit one token, done.
Failure modes
- If the price oracle is stale or manipulable, traders can drain the pool at a wrong price before it corrects.
- If inventory of the single token runs out on one side, the curve can widen sharply or trading halts, surprising users used to symmetric AMMs.
- Concentration risk: LPs are fully exposed to that one token's price collapse, unlike a paired pool that partially hedges via the other asset.
- Reflexive death spirals can occur if the deposited token is also the protocol's own governance or reward token and its price and liquidity depth are mutually reinforcing on the way down.
What to check before using it
- Confirm what oracle or pricing source drives the curve, its update frequency, and its manipulation resistance.
- Understand how the protocol behaves when one-sided inventory is nearly exhausted — does it halt, reprice sharply, or borrow externally?
- Check whether LP rewards compensate for full directional exposure to the single asset, not just trading fees.
- Verify audit history of the specific pricing curve implementation, since these are more custom (and less battle-tested) than a standard constant-product pool.