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About Engine

How are Engine and the thirdweb Contract SDK different?

Engine is a server that manages your backend wallets and how they interact with contracts. This difference unlocks capabilities that thirdweb and other web3 SDKs, including:

  • Management of KMS backend wallets
  • Fine-grained access control with access tokens
  • Transaction parallelization to handle higher throughput per wallet
  • Observability and retries on stuck transactions
  • Webhooks on completed transactions to sync on-chain and off-chain activity

Additionally, Engine is built on top of the thirdweb SDK and has the same capabilities.

Does Engine work with all thirdweb smart contracts?

Yes. Engine has intuitive interfaces to deploy prebuilt contracts, manage smart wallets, run a marketplace, and more.

Does Engine work with my non-thirdweb smart contract?

Yes. Engine can read and write to any EVM contract with low-level API calls, including providing raw calldata. ERC-721 and ERC-1155 APIs can also be used for contracts imported to thirdweb.

Using Engine

How do I wait for a transaction to be mined?

Write calls to contracts do not block until they are mined. Instead they enqueue an async job and immediately return a reference to the job called queueId.

Here are three ways to determine when the job is mined:

  • Use webhooks to notify your backend when a transaction event occurs.

  • Poll the /transaction/status/<queue_id> endpoint.

  • Use websockets:

    const socket = new WebSocket(
    socket.onmessage = (event) => {
    const res = JSON.parse(;
    console.log("Received data:", JSON.parse(res.result));

How do I cancel a transaction?

If a transaction is has not yet been mined or failed, cancel the transaction with POST /transaction/cancel.

Or to cancel a transaction in the Engine dashboard, select the Cancel transaction button next to the status in the Transactions table.

Cancel transaction button

How do I customize RPC URLs?

Set the CHAIN_OVERRIDES environment variable to the path to a JSON file or internet-accessible URL. The default value is ./chain-overrides.json if found. See the example format.


How do I resolve an "invalid password" error?

As of v0.0.7, an ENCRYPTION_PASSWORD is used to encrypt sensitive data stored in DB. Prior versions used the THIRDWEB_API_SECRET_KEY by default.

To resolve this error, set ENCRYPTION_PASSWORD to the THIRDWEB_API_SECRET_KEY used during setup.

Afterward you may change THIRDWEB_API_SECRET_KEY if needed. Do not change ENCRYPTION_PASSWORD since all sensitive data is encrypted with this password.

How do I resolve issues connecting to Postgres DB?

Here are some common troubleshooting tips:

  • Ensure the Postgres DB is running in Docker:
    • In same container, ensure the host in the POSTGRES_CONNECTION_URL is set to localhost.
    • In different container, ensure the host in the POSTGRES_CONNECTION_URL is set to host.docker.internal.
  • Ensure the Postgres DB connection URL and credentials are correct.
  • Ensure the database name exists on the Postgres DB.