# GraphQL Server

In addition to the [JSON-RPC APIs](/etn-sc-client/interacting-with-etn-sc/json-rpc-server.md), Etn-sc supports the GraphQL API as specified by [EIP-1767](https://eips.ethereum.org/EIPS/eip-1767). GraphQL lets you specify which fields of an objects you need as part of the query, eliminating the extra load on the client for filling in fields which are not needed. It also allows for combining several traditional JSON-RPC requests into one query which translates into less overhead and more performance.

The GraphQL endpoint piggybacks on the HTTP transport used by JSON-RPC. Hence the relevant `--http` flags and the `--graphql` flag should be passed to Etn-sc:

```sh
etn-sc --http --graphql
```

Now queries can be raised against `http://localhost:8545/graphql`. To change the port, provide a custom port number to `--http.port`, e.g.:

```sh
etn-sc --http --http.port 9545 --graphql
```

## GraphiQL <a href="#graphiql" id="graphiql"></a>

An easy way to try out queries is the GraphiQL interface shipped with Etn-sc. To open it visit `http://localhost:8545/graphql/ui`. To see how this works let's read the sender, recipient and value of all transactions in block number 6000000. In GraphiQL:

```graphql
query txInfo {
  block(number: 6000000) {
    transactions {
      hash
      from {
        address
      }
      to {
        address
      }
      value
    }
  }
}
```

GraphiQL also provides a way to explore the schema Etn-sc provides to help you formulate your queries, which you can see on the right sidebar. Under the title `Root Types` click on `Query` to see the high-level types and their fields.

## Query <a href="#query" id="query"></a>

Reading out data from Etn-sc is the biggest use-case for GraphQL. In addition to using the UI queries can also be sent programmatically. The official GraphQL [docs](https://graphql.org/code/) explain how to find bindings for many languages, or send http requests from the terminal using tools such as Curl.

For example, the code snippet below shows how to obtain the latest block number using Curl. Note the use of a JSON object for the data section:

```sh
❯ curl -X POST http://localhost:8545/graphql -H "Content-Type: application/json" --data '{ "query": "query { block { number } }" }'
{"data":{"block":{"number":"0x5b9d65"}}}
```

Alternatively store the JSON-ified query in a file (let's call it block-num.query) and do:

```sh
❯ curl -X POST http://localhost:8545/graphql -H "Content-Type: application/json" --data '@block-num.query'
```

Executing a simple query in JS looks as follows. Here the lightweight library `graphql-request` is used to perform the request. Note the use of variables instead of hardcoding the block number in the query:

```javascript
const { request, gql } = require('graphql-request');

const query = gql`
  query blockInfo($number: Long) {
    block(number: $number) {
      hash
      stateRoot
    }
  }
`;
request('http://localhost:8545/graphql', query, { number: '6004067' })
  .then(res => {
    console.log(res);
  })
  .catch(err => {
    console.log(err);
  });
```

## Accessing state <a href="#accessing-state" id="accessing-state"></a>

The schema allows for querying parts of state, i.e. accounts and their storage slots. E.g. it is possible to get the balance of the sender of a tx via:

```graphql
transaction(hash: "0xdad") {
    from {
        balance
    }
}
```

It is important to note however that the balance returned here is **not** the balance at the given transaction, rather it is the latest balance of the sender account, i.e. at the head of the chain. It is possible to query the state of this account at a particular block N via:

```graphql
transaction(hash: "0xdad") {
    from(block: 6004067) {
        balance
    }
}
```

As you can see this effect takes in a block number parameter which instructs Etn-sc to return the state of this account from an older block. The node needs to have the state for that block persisted, otherwise this query will result in an error. To see how Etn-sc persists state please see this [page](/etn-sc-client/developers/evm-tracing.md).


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://developer.electroneum.com/etn-sc-client/interacting-with-etn-sc/graphql-server.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.