Crypto Decentralized Exchanges: How It Works

A crypto decentralized exchange (DEX) is a system for arranging or executing trades in which at least part of the trading or settlement process is carried out through blockchain-based smart contracts rather than solely through a venue’s internal account ledger. The term covers multiple architectures, so the exact path from a user’s instruction to a completed trade depends on the design. An automated market maker (AMM) is one important model: smart contracts interact with liquidity pools, and a trade settles when its transaction is included in a blockchain block. (claim_bis_dex_contract_settlement)

The main contrast is with a centralized exchange (CEX), where a user typically transfers funds and custody to the venue before trading through its internal order book. That is a high-level model, not a description of every platform or product: custody, legal ownership, and settlement arrangements can vary. (claim_bis_cex_custody)

What Crypto Decentralized Exchanges means

“Decentralized exchange” does not identify one single technical design. It describes a family of systems whose execution, order coordination, or settlement may rely on blockchain contracts and related components. The public-permissionless DEX model in the source evidence allows users to retain control of assets while trades execute or settle through smart contracts on a blockchain. This does not mean every DEX interaction is free of intermediaries or off-chain services: interfaces, relayers, administrators, or off-chain order components may remain part of the system. (claim_bis_dex_distinction)

For an AMM DEX, a useful system boundary includes the user’s wallet and transaction, the smart contract, a liquidity pool, and the blockchain that processes and records the transaction. The contract and pool provide the trading mechanism; blockchain inclusion is the settlement event described in the accepted evidence. Other DEX families—including order-book, auction, intent-based, cross-chain, and hybrid designs—can follow different execution paths, so the AMM flow should not be treated as a universal DEX specification. (claim_bis_dex_contract_settlement)

The comparison with a CEX is therefore about where execution and custody sit, not a blanket judgment about which model is safer or more effective. A CEX can provide near-real-time trading, liquid order books, and advanced order functionality after assets are deposited, although performance and liquidity vary by venue, asset pair, and market conditions. (claim_bis_cex_fast_internal_trading)

Core components of Crypto Decentralized Exchanges

User and wallet. A user forms a trade instruction and uses a wallet to authorize the relevant blockchain transaction. In the public-permissionless model, the user can retain control of assets as trades execute or settle through smart contracts. That control boundary is specific to the model and does not establish that every interface, order path, or DEX design is entirely user-controlled. (claim_bis_dex_distinction)

Interface and transaction construction. A web or other interface can help a user inspect a trade and prepare a transaction. The interface is distinct from the contract that executes the on-chain logic. Because DEX designs can depend on interfaces, relayers, administrators, or off-chain order components, an operator should identify which parts are optional tools and which parts are necessary to the chosen route. (claim_bis_dex_distinction)

Smart contract and liquidity pool. In the AMM model covered by the source, smart contracts and liquidity pools implement trading. The pool is the mechanism through which that model makes assets available for the transaction; the contract applies the relevant execution logic. The source claim establishes this architecture at a high level, not the exact formula, fee schedule, or behavior of any particular pool. (claim_bis_dex_contract_settlement)

Blockchain and transaction inclusion. The chain processes the submitted transaction and records it in a block. For the specified AMM model, settlement occurs when the transaction is included in a blockchain block. This makes the chain a core dependency, rather than merely a recordkeeping layer after an exchange has completed an internal trade. (claim_bis_dex_contract_settlement)

Off-chain and administrative dependencies. Some DEX designs rely on services or components outside the contract, including interfaces, relayers, administrators, or off-chain order components. Their presence changes what “decentralized” means operationally: a contract may settle a trade while another component influences how the order is presented, routed, or made available. The accepted evidence supports checking for such dependencies, but does not specify the capabilities or authority of any particular service. (claim_bis_dex_distinction)

How Crypto Decentralized Exchanges works

A simplified AMM transaction can be understood as a sequence of checks and state changes. Exact steps, user prompts, and execution rules depend on the implementation.

  1. The user selects a route and trade. The user identifies the assets and intended trade through a wallet or an interface. If a route uses an interface, relayer, or off-chain order component, that component may be part of the practical path even though settlement for the AMM model occurs through a smart contract. (claim_bis_dex_distinction)
  2. A transaction is prepared and authorized. The transaction must be authorized by the user’s wallet before it can be submitted. The source establishes the user-control model at a broad level; it does not establish a universal approval sequence or specify wallet behavior for every DEX. Those details require implementation-specific inspection.
  3. The transaction is submitted to the blockchain. The transaction asks the relevant smart contract to perform the trade against a liquidity pool. This is distinct from placing an order solely on a CEX’s internal order book. In the AMM model, contracts and pools implement the trading mechanism. (claim_bis_dex_contract_settlement)
  4. The contract processes the trade. The contract applies its programmed logic to the transaction and pool. The accepted claim does not define a universal pricing formula, slippage control, fee, or transaction ordering rule. Those must be verified in the particular protocol’s documentation and implementation rather than inferred from the AMM label.
  5. The transaction is included in a block. For the AMM model described in the evidence, inclusion in a blockchain block is the settlement point. Before inclusion, the attempted transaction should not be described as settled under that definition. The source does not specify confirmation thresholds or chain-specific finality rules, which can differ by implementation and network.
  6. The resulting state can be checked. A technical review should compare the submitted transaction with its recorded outcome and the relevant contract and pool state. The precise evidence to inspect is chain- and protocol-specific; the broad mechanism alone does not establish that a trade succeeded as intended.

A CEX follows a different high-level pattern. A user typically transfers funds and custody to the venue, then trades through its internal order book. The venue can offer near-real-time trading, liquid order books, and advanced order functionality after deposit, subject to variation by venue, pair, and market conditions. This describes internal venue trading, not an assertion that every CEX product settles or holds assets in exactly the same way. (claim_bis_cex_custody) (claim_bis_cex_fast_internal_trading)

Trust and control boundaries

The central question is which party or component can act on assets, instructions, and execution. In the public-permissionless DEX model, the user can retain control of assets while trades execute or settle through smart contracts. This differs from the typical CEX model, in which the user transfers funds and custody to the exchange before using its internal order book. Both statements are qualified models: the evidence explicitly allows variation in DEX design and in CEX custody or settlement arrangements. (claim_bis_dex_distinction) (claim_bis_cex_custody)

Control of assets also does not equal control of every part of the transaction path. A user might retain assets while depending on an interface, relayer, administrator, or off-chain order component. A technical assessment should therefore distinguish at least three questions: who controls the assets before execution, what code or service determines the execution route, and what event counts as settlement. For the AMM model, the accepted answer to the last question is blockchain-block inclusion; other DEX designs can differ. (claim_bis_dex_contract_settlement) (claim_bis_dex_distinction)

CEX and DEX execution also place different functions inside or outside the venue. A CEX’s internal order book can support near-real-time trading and advanced order functionality after deposit, while the AMM model uses smart contracts and pools and settles through blockchain inclusion. Neither architecture by itself proves a particular service’s security, liquidity, performance, or recovery capability. Those properties require evidence about the specific venue, protocol, asset pair, and operating conditions. (claim_bis_cex_fast_internal_trading) (claim_bis_dex_contract_settlement)

Limitations and failure modes

A DEX label does not establish that the whole system is on-chain or that no party has operational influence. Interfaces, relayers, administrators, and off-chain order components can remain dependencies. A failure or change in one of these components may affect access or order routing even if the contract-based settlement mechanism is separate; the exact effect depends on the implementation and should not be assumed without evidence. (claim_bis_dex_distinction)

An AMM’s pool-and-contract model also does not, by itself, establish what price a user will receive, how much liquidity is available, what fees apply, or whether a transaction will be included. The accepted source claim identifies the mechanism and settlement point, not those transaction-level outcomes. Teams should verify the applicable contract logic and observed state rather than extrapolating from the general AMM description. (claim_bis_dex_contract_settlement)

A transaction that has not been included in a block has not reached the stated AMM settlement event. Inclusion alone, however, should not be presented as a universal assurance of finality, successful user intent, or recovery. The source pack does not provide chain-specific finality rules, confirmation requirements, or remedies for an unsuccessful transaction; those questions require evidence for the particular chain and protocol.

CEXs have different trade-offs rather than a single uniform profile. Their internal systems can support near-real-time trading and advanced order functionality, but performance and liquidity vary by venue, asset pair, and market conditions. The typical deposit-and-custody model also has stated exceptions, and custody or legal ownership can vary by platform and jurisdiction. A comparison should preserve those limits rather than treating “CEX” as a guarantee of a specific custody arrangement or execution quality. (claim_bis_cex_fast_internal_trading) (claim_bis_cex_custody)

What teams should verify

Before relying on a DEX route, technical and operational teams can use the following evidence-led checklist:

  • Identify the design. Determine whether the route is AMM-based, order-book, auction, intent-based, cross-chain, or hybrid. Do not apply the AMM settlement description to other designs without supporting documentation. (claim_bis_dex_contract_settlement)
  • Map the complete path. Record the wallet, interface, relayer, off-chain order components, administrator roles, smart contracts, pools, and blockchain involved. Mark which components are required for submitting, routing, executing, and settling a trade. (claim_bis_dex_distinction)
  • Locate asset control. Establish who controls the assets at each step and whether the route matches the public-permissionless model in which the user can retain control during execution or settlement. Check the actual design rather than assuming all DEXs share this property. (claim_bis_dex_distinction)
  • Define settlement evidence. For an AMM route covered by the source, identify the blockchain transaction and block inclusion that constitute settlement. Separately document any chain-specific confirmation or finality assumptions; the accepted claim does not supply them. (claim_bis_dex_contract_settlement)
  • Inspect implementation-specific behavior. Verify contract logic and the relevant pool state, along with any documented execution conditions. The source pack does not establish a common AMM formula, fee, or transaction outcome, so these must not be inferred from the category name.
  • Assess dependencies and fallback paths. Determine what happens operationally if an interface or relayer is unavailable, or if an off-chain order component or administrator is involved. The source identifies possible dependencies but does not prescribe their failure behavior. (claim_bis_dex_distinction)
  • Make comparisons on equivalent terms. For a CEX comparison, identify whether the product follows the typical model of user funds and custody moving to the venue before internal-order-book trading, while checking for product-specific exceptions. Compare execution and liquidity claims with their venue, pair, and market-condition qualifications. (claim_bis_cex_custody) (claim_bis_cex_fast_internal_trading)

The practical distinction is thus not simply “on-chain versus off-chain.” It is a map of custody, execution, dependencies, and settlement. An AMM DEX uses contracts and pools, with the described settlement event occurring at blockchain inclusion; a typical CEX uses deposited funds and an internal order book, with trading capabilities that vary by venue and conditions. For any concrete system, the architecture and its qualifications must be verified at the component level. (claim_bis_dex_contract_settlement) (claim_bis_cex_custody)

Sources and references