RPC Calls¶

Introduction¶

Remote Procedure Call (RPC) interfaces are the primary way to interact programmatically with Polkadot SDK-based parachains and relay chains. RPC calls allow you to query chain state, submit transactions, and monitor network health from external applications or scripts.

This guide covers:

What RPC calls are and how they work in the Polkadot SDK.
How to make RPC calls using curl or similar tools.
The most useful and commonly used RPC methods.

RPC endpoints are available on every node and can be accessed via HTTP and WebSocket. Most developer tools, dashboards, and libraries (like Polkadot.js, Subxt, and others) utilize these endpoints internally.

How Do RPC Calls Work?¶

RPC (Remote Procedure Call) is a protocol that allows you to invoke functions on a remote server (in this case, a blockchain node) as if they were local. Polkadot SDK nodes implement the JSON-RPC 2.0 standard, making it easy to interact with them using standard HTTP requests.

flowchart LR
CLIENT([Client Application])-- JSON-RPC Request -->NODE([Node])
NODE -- JSON Response --> CLIENT

RPC calls are stateless and can be used to:

Query chain state (e.g., block number, storage values)
Submit extrinsics (transactions)
Monitor node and network health
Retrieve metadata and runtime information

Making RPC Calls with Curl¶

You can make RPC calls to a node using curl or any HTTP client. The general format that the RPC calls stick to is the following:

curl -H "Content-Type: application/json" \
  -d '{"id":1, "jsonrpc":"2.0", "method": "INSERT_METHOD_NAME", "params": [INSERT_PARAMS]}' \
  NODE_ENDPOINT

method: The RPC method you want to call (e.g., system_health).
params: Parameters for the method (if any).
NODE_ENDPOINT: The HTTP endpoint of your node (e.g., http://localhost:9933 or a public endpoint).

Here's a simple example to get the latest block number of the Polkadot relay chain; you can use the following node endpoint:

curl -H "Content-Type: application/json" \
  -d '{"id":1, "jsonrpc":"2.0", "method": "chain_getBlock"}' \
  https://rpc.polkadot.io

Essential RPC Methods¶

Below are some of the most useful and commonly used RPC methods for Polkadot SDK-based chains. Each method includes a description, parameters, and an example request.

system_health¶

Checks the health of your node.

Parameters:

None

Example:

system_health

curl -H "Content-Type: application/json" \
    -d '{"id":1, "jsonrpc":"2.0", "method": "system_health", "params":[]}' \
    http://localhost:9933

chain_getBlock¶

Returns the latest block or a specific block by hash.

Parameters:

blockHash (optional, string) – The hash of the block to retrieve. If omitted, returns the latest block.

Example:

chain_getBlock

curl -H "Content-Type: application/json" \
    -d '{"id":1, "jsonrpc":"2.0", "method": "chain_getBlock", "params":[]}' \
    http://localhost:9933

state_getStorage¶

Queries on-chain storage by key (requires SCALE-encoded storage key).

Parameters:

storageKey (string) – The SCALE-encoded storage key to query.

Example:

state_getStorage

curl -H "Content-Type: application/json" \
    -d '{"id":1, "jsonrpc":"2.0", "method": "state_getStorage", "params":["0x..."]}' \
    http://localhost:9933

author_submitExtrinsic¶

Submits a signed extrinsic (transaction) to the node.

Parameters:

extrinsic (string) – The SCALE-encoded, signed extrinsic (transaction).

Example:

author_submitExtrinsic

curl -H "Content-Type: application/json" \
    -d '{"id":1, "jsonrpc":"2.0", "method": "author_submitExtrinsic", "params":["0x..."]}' \
    http://localhost:9933

state_getMetadata¶

Fetches the runtime metadata (needed for decoding storage and extrinsics).

Parameters:

None

Example:

state_getMetadata

curl -H "Content-Type: application/json" \
    -d '{"id":1, "jsonrpc":"2.0", "method": "state_getMetadata", "params":[]}' \
    http://localhost:9933

Check Available RPC Calls¶

To check all the RPC methods exposed by your node, you can use the rpc_methods call to get a comprehensive list of available methods. This is particularly useful when working with different chain implementations or custom runtimes that may have additional RPC endpoints. You can do this via curl or the Polkadot.Js Apps.

Using curl¶

To check the available RPC methods using curl, you can use the following command:

curl -H "Content-Type: application/json" \
  -d '{"id":1, "jsonrpc":"2.0", "method": "rpc_methods", "params":[]}' \
  https://rpc.polkadot.io

You can replace https://rpc.polkadot.io with the node endpoint you need to query.

Using Polkadot.js Apps¶

Go to the Polkadot.js Apps UI and navigate to the RPC calls section.
Select rpc from the dropdown menu.
Choose the methods method.
Submit the call to get a list of all available RPC methods.

This will return a JSON response containing all the RPC methods supported by your node.

From this interface, you can also query the RPC methods directly, as you would do with curl.

Resources¶

Last update: July 22, 2025
| Created: July 22, 2025