What a liquidity provider does, and why it matters to traders

Foreign exchange has no central exchange. Prices are made by dealers and passed down a chain of intermediaries until they appear, a few milliseconds later, on a retail trading screen. The firms at each link of that chain are loosely called liquidity providers, and the way a broker connects to them shapes the spreads, fills and rejections its clients see.

The top of the chain

At the top sit the large dealing banks, often called tier-one liquidity providers. They quote two-way prices in size across many currency pairs, hold inventory and manage the risk. Alongside them, non-bank market makers, including electronic trading firms, have become major price-makers in spot FX.

These firms will not deal directly with a small broker or fund. They extend credit only to counterparties they trust, and building that relationship requires capital, legal agreements and credit lines that most smaller firms cannot obtain.

Prime brokers and prime-of-prime

Prime brokerage solves the credit problem. A prime broker, usually a large bank, lets a client trade with many dealers in the prime broker’s name and on its credit. The dealers face the bank, not the small client, and the client settles everything through one relationship.

It is a big business. According to the Bank for International Settlements’ 2025 Triennial Survey, prime-brokered trades averaged about $2.2 trillion a day in April 2025, roughly 23% of all FX turnover.

The Swiss franc shock of January 2015 reshaped this corner of the market. When the Swiss National Bank abandoned its exchange rate floor, some prime brokers suffered heavy losses on accounts belonging to retail margin brokers. A BIS analysis published in 2019 described what followed: tighter credit and risk management, stricter onboarding and consolidation, with banks favouring larger clients. Smaller brokers and funds were pushed towards the prime-of-prime model, in which a well-capitalised intermediary holds the prime brokerage relationship and extends access to smaller firms beneath it.

For many retail brokers, a prime-of-prime provider is the practical route to institutional pricing.

Aggregation and bridges

A broker connected to several providers receives several competing price streams. An aggregator combines them into a single order book, typically showing the best bid and offer available at each moment and deciding where to send each order.

Retail trading platforms were not originally built to talk to institutional venues, so brokers use a bridge, software that sits between the platform and the liquidity side. The bridge takes client orders from the platform, applies the broker’s rules on markups, routing and risk, and forwards them to the aggregator or provider. It then returns the fills to the platform.

This is also where the broker’s execution model lives in practice. The bridge settings decide which orders are passed to external providers and which are kept in-house.

FIX: the common language

Most of these connections speak FIX, the Financial Information eXchange protocol. It began in 1992 as a way for Fidelity Investments and Salomon Brothers to replace telephone calls with machine-readable messages about equity orders, and it is now maintained by the non-profit FIX Trading Community as a standard across asset classes.

When a broker offers a “FIX API” to clients, it means professional traders can connect their own systems to its pricing and execution directly, without a retail platform in between.

Last look

Many liquidity providers use last look: a brief window after receiving a trade request in which they may accept or reject it at the quoted price. Providers argue it protects them against stale quotes and latency arbitrage. Critics say it can be abused.

The FX Global Code, the industry’s principles of good practice, addresses this in Principle 17. Firms using last look should be transparent about it and disclose how it works, including whether price moves in either direction affect the decision and how long the window typically lasts. The Code states that last look should be used only for validity and price checks, and that a provider should not trade on the information in a client’s request during the window.

Every link between the trader and the price-maker adds a decision, a markup or a delay.

Why it matters to traders

Most retail traders never see this machinery, but they feel it:

• Spreads reflect the prices a broker receives and the markup it adds.
• Rejections and requotes often trace back to last look at the provider level, or to broker-side rules.
• Slippage in fast markets depends on how deep the aggregated book is, and how many providers stay in when volatility rises.
• Resilience depends on the chain. A broker with one provider has one point of failure.

Useful questions for a broker include how many liquidity providers it uses, whether it relies on a prime-of-prime, and whether it has signed a statement of commitment to the FX Global Code. The answers say more about execution quality than any headline spread.