HTTP Endpoints - Lasso RPC

Overview

All HTTP RPC endpoints accept POST requests with Content-Type: application/json and follow the JSON-RPC 2.0 specification.

Base Endpoint

Routes requests using the default strategy (configurable, defaults to load_balanced).

POST /rpc/:chain

Parameters

:chain - Chain identifier (name or numeric ID)
- Chain name: ethereum, base, arbitrum
- Chain ID: 1, 8453, 42161

Example

curl -X POST http://localhost:4000/rpc/ethereum \
  -H 'Content-Type: application/json' \
  -d '{"jsonrpc":"2.0","method":"eth_blockNumber","params":[],"id":1}'

Response:

{
  "jsonrpc": "2.0",
  "id": 1,
  "result": "0x8471c9a"
}

Strategy Endpoints

Explicitly specify the routing strategy for provider selection.

Fastest

POST /rpc/fastest/:chain

Routes all requests to the single fastest provider based on measured latency.

curl -X POST http://localhost:4000/rpc/fastest/ethereum \
  -H 'Content-Type: application/json' \
  -d '{"jsonrpc":"2.0","method":"eth_blockNumber","params":[],"id":1}'

Load Balanced

POST /rpc/load-balanced/:chain
POST /rpc/round-robin/:chain

Randomly distributes requests across healthy providers.

curl -X POST http://localhost:4000/rpc/load-balanced/ethereum \
  -H 'Content-Type: application/json' \
  -d '{"jsonrpc":"2.0","method":"eth_getBalance","params":["0x123...","latest"],"id":1}'

Latency Weighted

POST /rpc/latency-weighted/:chain

Probabilistically routes requests with bias toward lower-latency providers.

curl -X POST http://localhost:4000/rpc/latency-weighted/ethereum \
  -H 'Content-Type: application/json' \
  -d '{"jsonrpc":"2.0","method":"eth_call","params":[{"to":"0x...","data":"0x..."},"latest"],"id":1}'

Provider Override Endpoints

Route directly to a specific provider, bypassing strategy selection.

POST /rpc/provider/:provider_id/:chain
POST /rpc/:chain/:provider_id

Parameters

:provider_id - Provider identifier (e.g., alchemy, infura, quicknode)
:chain - Chain identifier

Example

curl -X POST http://localhost:4000/rpc/provider/alchemy/ethereum \
  -H 'Content-Type: application/json' \
  -d '{"jsonrpc":"2.0","method":"eth_blockNumber","params":[],"id":1}'

Alternative syntax:

curl -X POST http://localhost:4000/rpc/ethereum/alchemy \
  -H 'Content-Type: application/json' \
  -d '{"jsonrpc":"2.0","method":"eth_blockNumber","params":[],"id":1}'

Profile-Scoped Endpoints

All routes above are available under a profile namespace for multi-tenancy.

POST /rpc/profile/:profile/:chain
POST /rpc/profile/:profile/fastest/:chain
POST /rpc/profile/:profile/load-balanced/:chain
POST /rpc/profile/:profile/latency-weighted/:chain
POST /rpc/profile/:profile/provider/:provider_id/:chain

Parameters

:profile - Profile slug (e.g., default, testnet, production)

Example

curl -X POST http://localhost:4000/rpc/profile/testnet/fastest/base \
  -H 'Content-Type: application/json' \
  -d '{"jsonrpc":"2.0","method":"eth_blockNumber","params":[],"id":1}'

Without an explicit profile in the URL, requests automatically use the "default" profile. Ensure config/profiles/default.yml exists at startup.

Supported Methods

Lasso supports read-only Ethereum JSON-RPC methods:

Block Methods

eth_blockNumber - Latest block number
eth_getBlockByNumber - Block data by number
eth_getBlockByHash - Block data by hash

Account Methods

eth_getBalance - Account balance
eth_getTransactionCount - Account nonce
eth_getCode - Contract bytecode

Transaction Methods

eth_getTransactionByHash - Transaction details
eth_getTransactionReceipt - Transaction receipt

Call Methods

eth_call - Read-only contract call
eth_estimateGas - Gas estimation

State Methods

eth_getLogs - Historical log queries
eth_getStorageAt - Storage slot value

Gas & Fee Methods

eth_gasPrice - Current gas price
eth_maxPriorityFeePerGas - EIP-1559 priority fee
eth_feeHistory - Historical fee data

Metadata Methods

eth_chainId - Chain ID (served locally, no upstream call)

Unsupported Methods

Subscription Methods

Subscription methods (eth_subscribe, eth_unsubscribe) are rejected over HTTP with a WebSocket URL hint:

{
  "jsonrpc": "2.0",
  "id": 1,
  "error": {
    "code": -32601,
    "message": "Method not supported over HTTP. Use WebSocket connection for subscriptions.",
    "data": {"websocket_url": "/ws/rpc/ethereum"}
  }
}

Write Methods

Write methods (eth_sendRawTransaction, eth_sendTransaction) are not currently supported.

Request Headers

Required Headers

Header	Value	Description
`Content-Type`	`application/json`	JSON request body

Optional Headers

Header	Example	Description
`X-Lasso-Api-Key`	`lasso_abc123`	API key authentication
`Authorization`	`Bearer lasso_abc123`	Bearer token authentication
`X-Lasso-Provider`	`alchemy`	Override provider selection
`X-Lasso-Transport`	`http` or `ws`	Force transport selection
`X-Lasso-Include-Meta`	`headers` or `body`	Request observability metadata

Provider Override Header

You can specify a provider via header instead of URL path:

curl -X POST http://localhost:4000/rpc/ethereum \
  -H 'Content-Type: application/json' \
  -H 'X-Lasso-Provider: alchemy' \
  -d '{"jsonrpc":"2.0","method":"eth_blockNumber","params":[],"id":1}'

Query Parameters

Parameter	Values	Description
`key`	`lasso_...`	API key for authentication
`include_meta`	`headers`, `body`	Return routing metadata
`transport`	`http`, `ws`	Force transport selection
`provider`	provider ID	Override provider selection
`strategy`	`fastest`, `load_balanced`, `latency_weighted`	Override routing strategy

Strategy Query Parameter

curl -X POST 'http://localhost:4000/rpc/ethereum?strategy=fastest' \
  -H 'Content-Type: application/json' \
  -d '{"jsonrpc":"2.0","method":"eth_blockNumber","params":[],"id":1}'

Response Format

Success Response

{
  "jsonrpc": "2.0",
  "id": 1,
  "result": "0x8471c9a"
}

Error Response

{
  "jsonrpc": "2.0",
  "id": 1,
  "error": {
    "code": -32602,
    "message": "Invalid params: unsupported chain"
  }
}

Error Codes

| Code | Meaning | |------|---------|| | -32700 | Parse error (malformed JSON) | | -32600 | Invalid Request (missing fields, batch too large) | | -32601 | Method not found or not supported on this transport | | -32602 | Invalid params (unsupported chain, missing chain_id) | | -32603 | Internal error | | -32000 | Server error (rate limit, strategy access denied, quota exceeded) |

Response Headers

Standard Headers

Header	Description
`Content-Type`	`application/json`
`X-Request-Id`	Phoenix request ID

Observability Headers

With include_meta=headers:

Header	Description
`X-Lasso-Request-ID`	Lasso request tracking ID
`X-Lasso-Meta`	Base64url-encoded routing metadata

CORS

All origins are allowed (*). Allowed headers:

Content-Type
Authorization
X-Requested-With
X-Lasso-Provider
X-Lasso-Transport
X-Lasso-Api-Key

Preflight responses are cached for 24 hours.

HTTP API

WebSocket API

Management API

Reference

​Overview

​Base Endpoint

​Parameters

​Example

​Strategy Endpoints

​Fastest

​Load Balanced

​Latency Weighted

​Provider Override Endpoints

​Parameters

​Example

​Profile-Scoped Endpoints

​Parameters

​Example

​Supported Methods

​Block Methods

​Account Methods

​Transaction Methods

​Call Methods

​State Methods

​Gas & Fee Methods

​Metadata Methods

​Unsupported Methods

​Subscription Methods

​Write Methods

​Request Headers

​Required Headers

​Optional Headers

​Provider Override Header

​Query Parameters

​Strategy Query Parameter

​Response Format

​Success Response

​Error Response

​Error Codes

​Response Headers

​Standard Headers

​Observability Headers

​CORS

Overview

Base Endpoint

Parameters

Example

Strategy Endpoints

Fastest

Load Balanced

Latency Weighted

Provider Override Endpoints

Parameters

Example

Profile-Scoped Endpoints

Parameters

Example

Supported Methods

Block Methods

Account Methods

Transaction Methods

Call Methods

State Methods

Gas & Fee Methods

Metadata Methods

Unsupported Methods

Subscription Methods

Write Methods

Request Headers

Required Headers

Optional Headers

Provider Override Header

Query Parameters

Strategy Query Parameter

Response Format

Success Response

Error Response

Error Codes

Response Headers

Standard Headers

Observability Headers

CORS