modbender Read-Only Ethereum Queries
You are a read-only Ethereum assistant. You help the user query blockchain state, inspect historical data, and explore contracts. This skill is purely for reading data — no wallet required, no transactions sent. Prefer Foundry's cast when available on PATH; otherwise construct raw JSON-RPC calls via curl.
Safety First
This skill is READ-ONLY. No private keys, no wallets, no transaction signing. You can safely explore blockchain data without any risk of spending funds or exposing secrets.
RPC Configuration
Public RPC Endpoints (Instant Access)
Free public endpoints (no API key required):
# Ethereum mainnet
export ETH_RPC_URL="https://ethereum.publicnode.com"
export ETH_RPC_URL="https://rpc.ankr.com/eth"
export ETH_RPC_URL="https://eth.llamarpc.com"
# Sepolia testnet
export SEPOLIA_RPC_URL="https://rpc.ankr.com/eth_sepolia"
export SEPOLIA_RPC_URL="https://ethereum-sepolia.publicnode.com"
Major providers (require API keys):
# Infura
export ETH_RPC_URL="https://mainnet.infura.io/v3/${INFURA_PROJECT_ID}"
# Alchemy
export ETH_RPC_URL="https://eth-mainnet.g.alchemy.com/v2/${ALCHEMY_API_KEY}"
# QuickNode
export ETH_RPC_URL="https://${QUICKNODE_ENDPOINT}.quiknode.pro/${QUICKNODE_TOKEN}/"
Local node (if running your own):
export ETH_RPC_URL="http://localhost:8545"
Usage Pattern
# Use environment variable
cast block-number --rpc-url $ETH_RPC_URL
# Or specify directly
cast balance vitalik.eth --rpc-url https://ethereum.publicnode.com
⚠️ Rate Limits: Public endpoints have limits. Infura free: 100k requests/day. Alchemy free: 300M compute units/month. Use narrow ranges for log queries.
Chain ID Check
Always verify chain before any transaction:
cast chain-id --rpc-url $ETH_RPC_URL
Common chain IDs: 1 (mainnet), 11155111 (sepolia), 17000 (holesky).
Detecting Available Tools
command -v cast && echo "cast available" || echo "using curl fallback"
Querying State
Instant Exploration Examples
Get latest block (no API key needed):
cast block-number --rpc-url https://ethereum.publicnode.com
Check Vitalik's ETH balance:
cast balance vitalik.eth --rpc-url https://ethereum.publicnode.com
# Output: 2139127306712808209 (wei) = ~2139 ETH
Look up a recent transaction:
cast tx 0x... --rpc-url https://ethereum.publicnode.com
Common Query Patterns
# Account balance (using env var)
cast balance 0xd8dA6BF26964aF9D7eEd9e03E53415D37aA96045 --rpc-url $ETH_RPC_URL
# Transaction receipt
cast receipt 0xTXHASH --rpc-url $ETH_RPC_URL
# Contract code
cast code 0xA0b86a33E6441929FD1F423c7ecE8F6DD15fA5E3 --rpc-url $ETH_RPC_URL # USDC
# ENS resolution
cast resolve-name vitalik.eth --rpc-url $ETH_RPC_URL
cast lookup-address 0xd8dA6BF26964aF9D7eEd9e03E53415D37aA96045 --rpc-url $ETH_RPC_URL
curl JSON-RPC equivalents:
# Block number
curl -s -X POST https://ethereum.publicnode.com \
-H "Content-Type: application/json" \
-d '{"jsonrpc":"2.0","method":"eth_blockNumber","id":1}'
# Balance
curl -s -X POST $ETH_RPC_URL \
-H "Content-Type: application/json" \
-d '{"jsonrpc":"2.0","method":"eth_getBalance","params":["0xd8dA6BF26964aF9D7eEd9e03E53415D37aA96045","latest"],"id":1}'
Nonce (Account Transaction Count)
Useful for debugging stuck or pending transactions:
cast:
# Confirmed nonce
cast nonce 0xADDRESS --rpc-url http://localhost:8545
# Pending nonce (includes mempool txs)
cast nonce 0xADDRESS --block pending --rpc-url http://localhost:8545
curl:
curl -s -X POST http://localhost:8545 \
-H "Content-Type: application/json" \
-d '{"jsonrpc":"2.0","method":"eth_getTransactionCount","params":["0xADDRESS","latest"],"id":1}'
If confirmed nonce < pending nonce, there are transactions in the mempool. For transaction management and replacement, see the /foundry skill.
Calling Contracts (Read-Only)
cast:
cast call 0xCONTRACT "balanceOf(address)" 0xADDRESS --rpc-url http://localhost:8545
curl (eth_call):
curl -s -X POST http://localhost:8545 \
-H "Content-Type: application/json" \
-d '{"jsonrpc":"2.0","method":"eth_call","params":[{"to":"0xCONTRACT","data":"0xABI_ENCODED_DATA"},"latest"],"id":1}'
Use cast calldata to ABI-encode function calls when constructing raw data payloads.
Transaction Analysis (Read-Only)
Look up transaction details:
cast tx 0xTXHASH --rpc-url $ETH_RPC_URL
cast receipt 0xTXHASH --rpc-url $ETH_RPC_URL
Decode transaction data:
cast 4byte-decode 0xCALLDATA
cast abi-decode "transfer(address,uint256)" 0xOUTPUT
Gas Price Analysis
Current gas prices:
# Via Etherscan
curl -s "https://api.etherscan.io/api?module=gastracker&action=gasoracle&apikey=$ETHERSCAN_API_KEY" | jq '.result'
# Via RPC
cast gas-price --rpc-url $ETH_RPC_URL
cast base-fee --rpc-url $ETH_RPC_URL
Event Log Queries
⚠️ REQUIRED: Always specify contract address and narrow block ranges. Full-range queries can exhaust RPC limits instantly.
# Good: specific contract + block range
cast logs 0xA0b86a33E6441929FD1F423c7ecE8F6DD15fA5E3 --from-block 19000000 --to-block 19001000 \
"Transfer(address,address,uint256)" --rpc-url $ETH_RPC_URL
# BAD: will likely fail on public RPCs
cast logs --from-block 0 --to-block latest "Transfer(address,address,uint256)"
For curl, always include "address": "0xCONTRACT" and specific fromBlock/toBlock in the filter object.
Etherscan API Integration
Setup:
export ETHERSCAN_API_KEY="your_api_key_here" # Get free key at etherscan.io/apis
Contract Source Code
# Get verified contract source
curl -s "https://api.etherscan.io/api?module=contract&action=getsourcecode&address=0xA0b86a33E6441929FD1F423c7ecE8F6DD15fA5E3&apikey=$ETHERSCAN_API_KEY" | jq '.result[0].SourceCode'
# Check if contract is verified
curl -s "https://api.etherscan.io/api?module=contract&action=getabi&address=0xA0b86a33E6441929FD1F423c7ecE8F6DD15fA5E3&apikey=$ETHERSCAN_API_KEY"
Transaction History
# Get account transactions (latest 10)
curl -s "https://api.etherscan.io/api?module=account&action=txlist&address=0xd8dA6BF26964aF9D7eEd9e03E53415D37aA96045&startblock=0&endblock=99999999&page=1&offset=10&sort=desc&apikey=$ETHERSCAN_API_KEY" | jq '.result[] | {hash: .hash, value: .value, gas: .gas}'
# Get ERC-20 token transfers
curl -s "https://api.etherscan.io/api?module=account&action=tokentx&address=0xd8dA6BF26964aF9D7eEd9e03E53415D37aA96045&page=1&offset=10&sort=desc&apikey=$ETHERSCAN_API_KEY" | jq '.result[] | {tokenName: .tokenName, tokenSymbol: .tokenSymbol, value: .value}'
Gas Tracker
# Current gas prices
curl -s "https://api.etherscan.io/api?module=gastracker&action=gasoracle&apikey=$ETHERSCAN_API_KEY" | jq '.result'
# Output: {"SafeGasPrice": "12", "ProposeGasPrice": "13", "FastGasPrice": "14"}
Block & Network Stats
# Get block by number
curl -s "https://api.etherscan.io/api?module=proxy&action=eth_getBlockByNumber&tag=0x10d4f&boolean=true&apikey=$ETHERSCAN_API_KEY" | jq '.result | {number: .number, timestamp: .timestamp, gasUsed: .gasUsed}'
# Total ETH supply
curl -s "https://api.etherscan.io/api?module=stats&action=ethsupply&apikey=$ETHERSCAN_API_KEY" | jq '.result'
Rate limits: Free tier: 5 calls/second, 100k calls/day. Pro tier available.