> ## Documentation Index
> Fetch the complete documentation index at: https://docs.sqd.dev/llms.txt
> Use this file to discover all available pages before exploring further.

<AgentInstructions>

## Submitting Feedback

If you encounter incorrect, outdated, or confusing documentation on this page, submit feedback:

POST https://docs.sqd.dev/feedback

```json
{
  "path": "/en/sdk/squid-sdk/how-to-start/squid-from-scratch",
  "feedback": "Description of the issue"
}
```

Only submit feedback when you have something specific and actionable to report.

</AgentInstructions>

# Indexer from scratch

> Build a Squid SDK indexer from scratch — learn how to compose evm-processor, typeorm-store, and graphql-server NPM packages without a starter template.

Here's an example of how SDK packages can be combined into a working indexer (called *squid*).

This page goes through all the technical details to make the squid architecture easier to understand. If you would like to get to a working indexer ASAP, [bootstrap from a template](/en/sdk/squid-sdk/how-to-start/squid-development#templates).

## USDT transfers API

<Info>
  **Pre-requisites**: NodeJS 20.x or newer, Docker.
</Info>

Suppose the task is to track transfers of USDT on Ethereum, then save the resulting data to PostgreSQL and serve it as a GraphQL API. From this description we can immediately put together a list of [packages](/en/sdk/squid-sdk/overview):

* `@subsquid/evm-processor` - for retrieving Ethereum data
* the triad of `@subsquid/typeorm-store`, `@subsquid/typeorm-codegen` and `@subsquid/typeorm-migration` - for saving data to PostgreSQL

We also assume the following choice of *optional* packages:

* `@subsquid/evm-typegen` - for decoding Ethereum data and useful constants such as event topic0 values
* `@subsquid/evm-abi` - as a peer dependency for the code generated by `@subsquid/evm-typegen`
* `@subsquid/graphql-server` / [OpenReader](/en/sdk/squid-sdk/reference/openreader-server)

To make the indexer, follow these steps:

<Steps>
  <Step title="Create a new folder and initialise a new project">
    * create `package.json`
      ```bash theme={"system"}
      npm init
      ```
    * add `.gitignore`
      ```bash title=".gitignore" theme={"system"}
      node_modules
      lib
      ```
  </Step>

  <Step title="Install the packages">
    ```bash theme={"system"}
    npm i dotenv typeorm @subsquid/evm-processor @subsquid/typeorm-store @subsquid/typeorm-migration @subsquid/graphql-server @subsquid/evm-abi
    ```

    ```bash theme={"system"}
    npm i typescript @subsquid/typeorm-codegen @subsquid/evm-typegen --save-dev
    ```
  </Step>

  <Step title="Add a minimal `tsconfig.json`">
    ```json title="tsconfig.json" theme={"system"}
    {
      "compilerOptions": {
        "rootDir": "src",
        "outDir": "lib",
        "module": "commonjs",
        "target": "es2020",
        "esModuleInterop": true,
        "skipLibCheck": true,
        "experimentalDecorators": true,
        "emitDecoratorMetadata": true
      }
    }
    ```
  </Step>

  <Step title="Define the schema for both the database and the core GraphQL API">
    Define the schema for both the database and the core GraphQL API in [`schema.graphql`](/en/sdk/squid-sdk/reference/schema-file):

    ```graphql title="schema.graphql" theme={"system"}
    type Transfer @entity {
      id: ID!
      from: String! @index
      to: String! @index
      value: BigInt!
    }
    ```
  </Step>

  <Step title="Generate TypeORM classes based on the schema">
    ```bash theme={"system"}
    npx squid-typeorm-codegen
    ```

    The TypeORM classes are now available at `src/model/index.ts`.
  </Step>

  <Step title="Prepare the database">
    * create `.env` and `docker-compose.yaml` files
      ```bash title=".env" theme={"system"}
      DB_NAME=squid
      DB_PORT=23798
      RPC_ETH_HTTP=https://rpc.ankr.com/eth
      ```
      ```yaml title="docker-compose.yaml" theme={"system"}
      services:
        db:
          image: postgres:15
          environment:
            POSTGRES_DB: "${DB_NAME}"
            POSTGRES_PASSWORD: postgres
          ports:
            - "${DB_PORT}:5432"
      ```
    * start the database container
      ```bash theme={"system"}
      docker compose up -d
      ```
    * compile the TypeORM classes
      ```bash theme={"system"}
      npx tsc
      ```
    * generate the migration file
      ```bash theme={"system"}
      npx squid-typeorm-migration generate
      ```
    * apply the migration with
      ```bash theme={"system"}
      npx squid-typeorm-migration apply
      ```
  </Step>

  <Step title="Generate utility classes for decoding USDT contract data">
    [Generate utility classes](/en/sdk/squid-sdk/resources/tools/typegen/generation) for decoding [USDT contract](https://etherscan.io/address/0xdac17f958d2ee523a2206206994597c13d831ec7) data based on its ABI.

    * Create an `./abi` folder:
      ```bash theme={"system"}
      mkdir abi
      ```

    * Find the ABI at the ["Contract" tab of the contract page on Etherscan](https://etherscan.io/address/0xdAC17F958D2ee523a2206206994597C13D831ec7#code). Scroll down a bit:

    * Copy the ABI, then paste to a new file at `./abi/usdt.json`.

    * Run the utility classes generator:
      ```bash theme={"system"}
      npx squid-evm-typegen src/abi ./abi/*
      ```

    The utility classes are now available at `src/abi/usdt.ts`
  </Step>

  <Step title="Tie all the generated code together with `src/main.ts`">
    Tie all the generated code together with a `src/main.ts` executable with the following code blocks:

    * Imports
      ```ts theme={"system"}
      import { EvmBatchProcessor } from '@subsquid/evm-processor'
      import { TypeormDatabase } from '@subsquid/typeorm-store'
      import * as usdtAbi from './abi/usdt'
      import { Transfer } from './model'
      ```
    * [`EvmBatchProcessor`](/en/sdk/squid-sdk/reference/processors/evm-batch) object definition
      ```ts theme={"system"}
      const processor = new EvmBatchProcessor()
        .setGateway('https://v2.archive.subsquid.io/network/ethereum-mainnet')
        .setRpcEndpoint({
          url: process.env.RPC_ETH_HTTP,
          rateLimit: 10
        })
        .setFinalityConfirmation(75) // 15 mins to finality
        .addLog({
          address: [ '0xdAC17F958D2ee523a2206206994597C13D831ec7' ],
          topic0: [ usdtAbi.events.Transfer.topic ]
        })
      ```
    * [`TypeormDatabase`](/en/sdk/squid-sdk/reference/store/typeorm) object definition
      ```ts theme={"system"}
      const db = new TypeormDatabase()
      ```
    * A call to [`processor.run()`](/en/sdk/squid-sdk/reference/processors/architecture#processorrun) with an inline definition of the [batch handler](/en/sdk/squid-sdk/reference/processors/architecture#batch-context)
      ```ts theme={"system"}
      processor.run(db, async ctx => {
        const transfers: Transfer[] = []
        for (let block of ctx.blocks) {
          for (let log of block.logs) {
            let {from, to, value} = usdtAbi.events.Transfer.decode(log)
            transfers.push(new Transfer({
              id: log.id,
              from, to, value
            }))
          }
        }
        await ctx.store.insert(transfers)
      })
      ```
      Note how supplying a `TypeormDatabase` to the function caused `ctx.store` to be a [PostgreSQL-compatible `Store` object](/en/sdk/squid-sdk/reference/store/typeorm#store-interface).
  </Step>

  <Step title="Compile the project and start the processor process">
    Compile the project and start the [processor process](/en/sdk/squid-sdk/overview#processor)

    ```bash theme={"system"}
    npx tsc
    ```

    ```bash theme={"system"}
    node -r dotenv/config lib/main.js
    ```
  </Step>

  <Step title="Start the GraphQL server">
    In a separate terminal, configure the GraphQL port and start the GraphQL server:

    ```diff title=".env" theme={"system"}
     DB_NAME=squid
     DB_PORT=23798
     RPC_ETH_HTTP=https://rpc.ankr.com/eth
    +GRAPHQL_SERVER_PORT=4350
    ```

    ```bash theme={"system"}
    npx squid-graphql-server
    ```
  </Step>
</Steps>

The finished GraphQL API with GraphiQL is available at [localhost:4350/graphql](http://localhost:4350/graphql).

Final code for this mini-tutorial is available in [this repo](https://github.com/subsquid-labs/squid-from-scratch).

<Tip>
  The commands listed here are often abbreviated as [custom `sqd` commands](/en/sdk/squid-sdk/squid-cli/commands-json) in squids. If you'd like to do that too you can use the [`commands.json` file of the EVM template](https://github.com/subsquid-labs/squid-evm-template/blob/main/commands.json) as a starter.
</Tip>