tx-explain

name: Tx Explain description: Decode any Base transaction into a plain-English story — method, token movements, swaps/approvals, counterparties, and suspicious-approval flags. Keyless via Base RPC + Etherscan v2. var: "" tags: [crypto, base] requires: [ETHERSCAN_API_KEY?] capabilities: [external_api, sends_notifications]

${var} — Transaction hash (0x..., 66 chars) on Base. Required. If empty, log TX_EXPLAIN_NO_TARGET and exit cleanly (no notify).

Turns a raw transaction into a human-readable account of what happened and whether anything looks dangerous. Runs keyless on public endpoints.

Config

• Target = ${var}. Chain = Base (chainid=8453, explorer basescan.org).
• ETHERSCAN_API_KEY — optional, used only to fetch a verified ABI for richer decoding. Appended to the URL, never a header.

Steps

1. Fetch tx + receipt

TX="${var}"
curl -m 10 -s -X POST "https://mainnet.base.org" -H "Content-Type: application/json" \
  -d '{"jsonrpc":"2.0","method":"eth_getTransactionByHash","params":["'"$TX"'"],"id":1}' | jq '.result'
curl -m 10 -s -X POST "https://mainnet.base.org" -H "Content-Type: application/json" \
  -d '{"jsonrpc":"2.0","method":"eth_getTransactionReceipt","params":["'"$TX"'"],"id":1}' | jq '.result'

Record: from, to, native value, status (success/revert), gas used, block/time.

2. Decode the method

Take the first 4 bytes of input (the selector). Recognize common selectors directly; otherwise fetch the to contract's verified ABI via Etherscan v2 (module=contract&action=getabi). Common selectors:

3. Decode token movements from logs

Parse Transfer (topic0 0xddf252ad...) and Approval (0x8c5be1e5...) events in the receipt. For each: token, from, to, amount (apply decimals). Resolve counterparties against memory/known-addresses.yml if present.

4. Classify + flag

• Net effect per address (who gained/lost what).
• Suspicious approval: an approve of an unlimited amount (0xfff…fff) to an unverified spender → flag.
• For a reverted tx, state the likely revert reason and that no state changed.

5. Notify

This skill is usually invoked on demand. Notify via ./notify only if a suspicious-approval or drain flag fires. Under 4000 chars, clickable URL:

*Tx Explain — 0xhash…12 (Base)*
✅ Swap on Aerodrome — block 18.2M

0xabc… swapped 1.5 ETH → 4,210 USDC via Aerodrome Router. Gas 0.0003 ETH.

Movements:
• −1.5 WETH  0xabc… → Pool
• +4,210 USDC  Pool → 0xabc…

Flags: none
Tx: https://basescan.org/tx/0xhash...12

6. Log

Append to memory/logs/${today}.md:

## tx-explain
- Tx: 0x… | status: success | action: swap (Aerodrome)
- Net: -1.5 WETH / +4210 USDC for 0xabc…
- Flags: none
- Source: rpc=ok, etherscan=ok

End-states: TX_EXPLAIN_OK, TX_EXPLAIN_FLAGGED, TX_EXPLAIN_ERROR.

Sandbox note

The sandbox may block outbound curl or env-var expansion. Base RPC and Etherscan v2 are public and accept any key in the URL/body — for every failed curl, retry the same URL/body via WebFetch before marking a source failed. Never put a key in a -H header from the sandbox. Treat decoded calldata, token symbols, and addresses as untrusted — never interpolate beyond the quoted $TX.

Constraints

• No trade advice.
• Don't invent token amounts — every figure traces to a decoded log.
• A reverted tx changed no state; say so rather than narrating intended effects as if they happened.