How to build a dApp: architecture, contracts and deployment

A decentralized application, or dApp, makes blockchain functionality available through an interface. Users can view information, connect a wallet or request a transaction, while smart contracts execute the rules assigned to the network. Building that experience involves connecting the application to its contracts and supporting services.

The design starts by deciding which parts of the process need to be verifiable on-chain and which remain in the application outside the network. That separation helps define user permissions and explain what happens before, during and after a transaction.

1. Define the operation requiring shared verification

Choose a concrete journey: recording evidence, transferring an asset or applying a rule between participants. Identify who can initiate it, the expected outcome and what another party must verify. Compare that objective with a conventional application before accepting the cost of a chain.

Ethereum's introduction to dApps describes frontends combined with contracts. Real products may also use indexers, storage and servers. Documenting those dependencies explains which functions remain available when a provider fails.

2. Separate contracts, interfaces and backends

Contracts maintain rules and state that need to be shared. Interfaces prepare requests and explain their consequences. Backends can handle search, notifications or private information. A backend should not silently become the sole authority for a property described as independently verifiable on-chain.

For example, a document registry can retain files in permissioned storage while recording hashes and authors on-chain. This supports later matching; it does not establish that the original document was true or that its signer had legal authority.

3. Choose a network and libraries

Assess finality, fees, permissions, supported wallets and team capabilities. Include the security assumptions of bridges or additional layers. For EVM networks, libraries such as viem support contract interaction, including reading state and preparing operations.

Pin versions and test the wallets your audience actually uses. Nominal compatibility does not replace tests for connection, account switching, signature rejection and transaction submission. Show the network and operation the user is authorising.

4. Specify permissions and invariants before implementation

Define who can administer, pause or upgrade contracts and the limits of each role. An invariant describes a property that should always hold, such as a withdrawal never exceeding the available balance.

Ethereum's contract testing guide describes complementary techniques. Use unit, integration and property tests where they provide evidence. Include unauthorised actors, unexpected responses and dependency failures; testing only the successful journey omits valuable cases.

5. Design transaction states

• Prepared: the user can inspect the recipient, amount and permissions.
• Awaiting signature: the user can accept or reject without losing context.
• Submitted: the interface keeps a verifiable reference and avoids duplicate submission.
• Confirmed or failed: explain the outcome and the available next step.

Do not present a pending operation as final. Do not place private keys in frontend code or logs. Key management, node configuration and server limits need review alongside contracts.

Integration example: recording evidence without duplication

Imagine a dApp that records a document hash. The user selects a file, reviews the operation and signs. If they close the tab after submission, they should be able to recover that request’s status on returning. Showing an empty form and prompting another submission can create two records for one intention.

The design needs to connect the business request, transaction reference and result observed on the network. If the RPC provider becomes unavailable, the application should explain that it cannot query the status, rather than assert that the operation failed. A failed query and a contract rejection require different responses.

Acceptance testing covers both a lost response after submission and an actually rejected transaction. It also verifies that another participant can check the recorded hash and that the application retains the file with the intended permissions. This is an implementation example; recording a hash does not establish a document’s legal authenticity.

The journey helps define which parts belong in contract review and which need integration testing. The experience depends on both, especially when an operation takes longer than expected or the user changes devices.

6. Deploy an identifiable version and prepare operations

Keep the repository, tests, audit report and published addresses traceable. For upgradeable systems, explain administrator powers and test the upgrade process. Users should understand which rules can change.

After launch, monitoring, incident handling and integration maintenance remain necessary. At Metlabs, blockchain application development brings those components together into an operable product with documented limits and responsibilities.