|
| 1 | +--- |
| 2 | +title: RPC Calls to Polkadot SDK chains. |
| 3 | +description: Learn how to interact with Polkadot SDK-based chains using RPC calls. This guide covers essential methods and usage via curl. |
| 4 | +--- |
| 5 | + |
| 6 | +# RPC Calls |
| 7 | + |
| 8 | +## Introduction |
| 9 | + |
| 10 | +[Remote Procedure Call](https://en.wikipedia.org/wiki/Remote_procedure_call){target=\_blank} (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. |
| 11 | + |
| 12 | +This guide covers: |
| 13 | + |
| 14 | +- What RPC calls are and how they work in the Polkadot SDK. |
| 15 | +- How to make RPC calls using `curl` or similar tools. |
| 16 | +- The most useful and commonly used RPC methods. |
| 17 | + |
| 18 | +RPC endpoints are available on every node and can be accessed via HTTP and WebSocket. Most developer tools, dashboards, and libraries (like [Polkadot.js](/develop/toolkit/api-libraries/polkadot-js-api){target=\_blank}, [Subxt](/develop/toolkit/api-libraries/subxt){target=\_blank}, and others) utilize these endpoints internally. |
| 19 | + |
| 20 | +## How Do RPC Calls Work? |
| 21 | + |
| 22 | +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](https://www.jsonrpc.org/specification){target=\_blank} standard, making it easy to interact with them using standard HTTP requests. |
| 23 | + |
| 24 | +```mermaid |
| 25 | +flowchart LR |
| 26 | +CLIENT([Client Application])-- JSON-RPC Request -->NODE([Node]) |
| 27 | +NODE -- JSON Response --> CLIENT |
| 28 | +``` |
| 29 | + |
| 30 | +RPC calls are stateless and can be used to: |
| 31 | + |
| 32 | +- Query chain state (e.g., block number, storage values) |
| 33 | +- Submit extrinsics (transactions) |
| 34 | +- Monitor node and network health |
| 35 | +- Retrieve metadata and runtime information |
| 36 | + |
| 37 | +## Making RPC Calls with Curl |
| 38 | + |
| 39 | +You can make RPC calls to a node using [`curl`](https://curl.se/){target=\_blank} or any HTTP client. The general format that the RPC calls stick to is the following: |
| 40 | + |
| 41 | +```bash |
| 42 | +curl -H "Content-Type: application/json" \ |
| 43 | + -d '{"id":1, "jsonrpc":"2.0", "method": "INSERT_METHOD_NAME", "params": [INSERT_PARAMS]}' \ |
| 44 | + NODE_ENDPOINT |
| 45 | +``` |
| 46 | + |
| 47 | +- **`method`**: The RPC method you want to call (e.g., `system_health`). |
| 48 | +- **`params`**: Parameters for the method (if any). |
| 49 | +- **`NODE_ENDPOINT`**: The HTTP endpoint of your node (e.g., `http://localhost:9933` or a public endpoint). |
| 50 | + |
| 51 | +Here's a simple example to get the latest block number of the Polkadot relay chain; you can use the following node endpoint: |
| 52 | + |
| 53 | +```bash |
| 54 | +curl -H "Content-Type: application/json" \ |
| 55 | + -d '{"id":1, "jsonrpc":"2.0", "method": "chain_getBlock"}' \ |
| 56 | + https://rpc.polkadot.io |
| 57 | +``` |
| 58 | + |
| 59 | +## Essential RPC Methods |
| 60 | + |
| 61 | +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. |
| 62 | + |
| 63 | +--- |
| 64 | + |
| 65 | +### system_health |
| 66 | + |
| 67 | +Checks the health of your node. |
| 68 | + |
| 69 | +**Parameters:** |
| 70 | + |
| 71 | +None |
| 72 | + |
| 73 | +**Example:** |
| 74 | + |
| 75 | +```bash title="system_health" |
| 76 | +curl -H "Content-Type: application/json" \ |
| 77 | + -d '{"id":1, "jsonrpc":"2.0", "method": "system_health", "params":[]}' \ |
| 78 | + http://localhost:9933 |
| 79 | +``` |
| 80 | + |
| 81 | +--- |
| 82 | + |
| 83 | +### chain_getBlock |
| 84 | + |
| 85 | +Returns the latest block or a specific block by hash. |
| 86 | + |
| 87 | +**Parameters:** |
| 88 | + |
| 89 | +- `blockHash` *(optional, string)* – The hash of the block to retrieve. If omitted, returns the latest block. |
| 90 | + |
| 91 | +**Example:** |
| 92 | + |
| 93 | +```bash title="chain_getBlock" |
| 94 | +curl -H "Content-Type: application/json" \ |
| 95 | + -d '{"id":1, "jsonrpc":"2.0", "method": "chain_getBlock", "params":[]}' \ |
| 96 | + http://localhost:9933 |
| 97 | +``` |
| 98 | + |
| 99 | +--- |
| 100 | + |
| 101 | +### state_getStorage |
| 102 | + |
| 103 | +Queries on-chain storage by key (requires [SCALE-encoded](/polkadot-protocol/parachain-basics/data-encoding){target=_blank} storage key). |
| 104 | + |
| 105 | +**Parameters:** |
| 106 | + |
| 107 | +- `storageKey` *(string)* – The SCALE-encoded storage key to query. |
| 108 | + |
| 109 | +**Example:** |
| 110 | + |
| 111 | +```bash title="state_getStorage" |
| 112 | +curl -H "Content-Type: application/json" \ |
| 113 | + -d '{"id":1, "jsonrpc":"2.0", "method": "state_getStorage", "params":["0x..."]}' \ |
| 114 | + http://localhost:9933 |
| 115 | +``` |
| 116 | + |
| 117 | +--- |
| 118 | + |
| 119 | +### author_submitExtrinsic |
| 120 | + |
| 121 | +Submits a signed extrinsic (transaction) to the node. |
| 122 | + |
| 123 | +**Parameters:** |
| 124 | + |
| 125 | +- `extrinsic` *(string)* – The SCALE-encoded, signed extrinsic (transaction). |
| 126 | + |
| 127 | +**Example:** |
| 128 | + |
| 129 | +```bash title="author_submitExtrinsic" |
| 130 | +curl -H "Content-Type: application/json" \ |
| 131 | + -d '{"id":1, "jsonrpc":"2.0", "method": "author_submitExtrinsic", "params":["0x..."]}' \ |
| 132 | + http://localhost:9933 |
| 133 | +``` |
| 134 | + |
| 135 | +--- |
| 136 | + |
| 137 | +### state_getMetadata |
| 138 | + |
| 139 | +Fetches the runtime metadata (needed for decoding storage and extrinsics). |
| 140 | + |
| 141 | +**Parameters:** |
| 142 | + |
| 143 | +None |
| 144 | + |
| 145 | +**Example:** |
| 146 | + |
| 147 | +```bash title="state_getMetadata" |
| 148 | +curl -H "Content-Type: application/json" \ |
| 149 | + -d '{"id":1, "jsonrpc":"2.0", "method": "state_getMetadata", "params":[]}' \ |
| 150 | + http://localhost:9933 |
| 151 | +``` |
| 152 | + |
| 153 | +--- |
| 154 | + |
| 155 | +## Check Available RPC Calls |
| 156 | + |
| 157 | +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`](#using-curl) or the [Polkadot.Js Apps](#using-polkadotjs-apps). |
| 158 | + |
| 159 | +### Using curl |
| 160 | + |
| 161 | +To check the available RPC methods using `curl`, you can use the following command: |
| 162 | + |
| 163 | +```bash |
| 164 | +curl -H "Content-Type: application/json" \ |
| 165 | + -d '{"id":1, "jsonrpc":"2.0", "method": "rpc_methods", "params":[]}' \ |
| 166 | + https://rpc.polkadot.io |
| 167 | +``` |
| 168 | + |
| 169 | +You can replace `https://rpc.polkadot.io` with the node endpoint you need to query. |
| 170 | + |
| 171 | +### Using Polkadot.js Apps |
| 172 | + |
| 173 | +1. Go to the [Polkadot.js Apps UI](https://polkadot.js.org/apps){target=\_blank} and navigate to the RPC calls section. |
| 174 | + |
| 175 | +  |
| 176 | + |
| 177 | +2. Select **`rpc`** from the dropdown menu. |
| 178 | + |
| 179 | +  |
| 180 | + |
| 181 | +3. Choose the **`methods`** method. |
| 182 | + |
| 183 | +  |
| 184 | + |
| 185 | +4. Submit the call to get a list of all available RPC methods. |
| 186 | + |
| 187 | +  |
| 188 | + |
| 189 | +This will return a JSON response containing all the RPC methods supported by your node. |
| 190 | + |
| 191 | + |
| 192 | + |
| 193 | +From this interface, you can also query the RPC methods directly, as you would do with curl. |
| 194 | + |
| 195 | +## Resources |
| 196 | + |
| 197 | +- [Polkadot JSON-RPC API Reference](https://polkadot.js.org/docs/substrate/rpc/){target=\_blank} |
| 198 | +- [Parity DevOps: Important Flags for Running an RPC Node](https://paritytech.github.io/devops-guide/guides/rpc_index.html?#important-flags-for-running-an-rpc-node){target=\_blank} |
| 199 | +- [Polkadot.js Apps RPC Explorer](https://polkadot.js.org/apps/#/rpc){target=\_blank} |
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