onchain-monitor

type	Skill
name	Onchain Monitor
category	crypto
description	Monitor blockchain addresses and contracts for notable activity
var
tags	["crypto"]
requires	["ALCHEMY_API_KEY?","COINGECKO_API_KEY?","ETHERSCAN_API_KEY?"]
capabilities	["external_api","sends_notifications"]

${var} — Watch label or chain to check. Empty = all watches. add-address:<0x… [chain]> is the shape the Telegram force-reply sends — it appends a new watch and exits (see step 0).

If ${var} is set, only monitor the watch with that label or watches on that chain.

Config

Reads memory/on-chain-watches.yml. If the file is missing or watches: [], offer to add the first watch via a Telegram force-reply (only if no add-address prompt was offered in the last 2 days of memory/logs/ — dedup so an unconfigured fork isn't nagged every run), then log ON_CHAIN_NO_CONFIG and exit cleanly (do not send an alert — empty config is not an error):

./notify "No addresses on watch yet. Paste one to monitor — a 0x… wallet, optionally its chain." \
  --force-reply --placeholder "0x… base" \
  --context "onchain-monitor::add-address"

The reply routes back as var=add-address:<0x… [chain]>, handled by the config-capture branch in step 0. Record FORCE_REPLY_OFFERED: add-address in the log when you send it.

# memory/on-chain-watches.yml
watches:
  - label: My Wallet
    address: "0x1234...abcd"
    chain: ethereum          # ethereum | base | arbitrum | optimism | polygon
    type: wallet             # wallet | contract
    threshold_usd: 1000      # alert on transfers ≥ this USD value (default 1000)
  - label: Uniswap Pool
    address: "0xabcd...5678"
    chain: ethereum
    type: contract
    event_topics:            # optional — only alert on these topic0 hashes
      - "0xddf252ad..."      # ERC20 Transfer

Optional memory/known-addresses.yml — counterparty label dictionary used to humanize alerts. Lowercase keys, free-text values:

labels:
  "0x28c6c06298d514db089934071355e5743bf21d60": "Binance 14"
  "0xa9d1e08c7793af67e9d92fe308d5697fb81d3e43": "Coinbase 10"
  "0xe592427a0aece92de3edee1f18e0157c05861564": "Uniswap V3 Router"
  "0x0000000000000000000000000000000000000000": "Zero (mint/burn)"

State

memory/on-chain-state.json — per-watch state, persisted atomically after each successful run:

{
  "My Wallet": {
    "last_block": 19345678,
    "last_run": "2026-04-20T12:00:00Z",
    "alerted_tx": ["0xabc...", "0xdef..."],
    "median_usd_30d": 8500
  }
}

• last_block — start block for the next run's fetch. Initialise to current_block − 2400 (≈ 8h ETH) on first run.
• alerted_tx — tx hashes alerted in last 7 days, capped at 200. Used for cross-run dedup.
• median_usd_30d — rolling median USD size of transfers at this watch; powers the WHALE-TRANSFER tag.

Write the file via mv from a tempfile so a mid-run failure cannot corrupt state.

Steps

Read memory/MEMORY.md, memory/on-chain-watches.yml, memory/on-chain-state.json, and the last 2 days of memory/logs/ (for visibility only — state lives in the JSON file).

0. Config capture (Telegram force-reply)

Before the per-watch loop, intercept the add-a-watch reply. When ${var} starts with add-address:, the operator replied to the force-reply prompt (offered in the Config section on an empty config) — append a watch and exit (no monitoring this invocation). The remainder is <address> [chain]:

case "${var}" in
  add-address:*)
    REST="$(printf '%s' "${var#add-address:}" | sed 's/^[[:space:]]*//')"
    ADDR="$(printf '%s' "$REST" | awk '{print $1}')"
    CHAIN="$(printf '%s' "$REST" | awk '{print tolower($2)}')"; CHAIN="${CHAIN:-ethereum}"
    case "$CHAIN" in ethereum|base|arbitrum|optimism|polygon) ;; *) CHAIN=ethereum ;; esac
    if ! printf '%s' "$ADDR" | grep -qiE '^0x[0-9a-f]{40}$'; then
      ./notify "Couldn't read \"$ADDR\" as an address. Reply with a 0x… wallet, optionally a chain."
      exit 0
    fi
    mkdir -p memory; touch memory/on-chain-watches.yml
    # Normalize an empty inline list so we can append block items, and ensure a watches: key exists.
    sed -i.bak -E 's/^watches:[[:space:]]*\[\][[:space:]]*$/watches:/' memory/on-chain-watches.yml && rm -f memory/on-chain-watches.yml.bak
    grep -q '^watches:' memory/on-chain-watches.yml || printf 'watches:\n' >> memory/on-chain-watches.yml
    if grep -qi "$ADDR" memory/on-chain-watches.yml; then
      ./notify 
    
      SHORT=
       >> memory/on-chain-watches.yml <<
      ./notify 
    
    
     0 ;;

Defaults for a captured watch: type: wallet, threshold_usd: 1000, label = the shortened address. The operator refines chain/type/threshold by editing memory/on-chain-watches.yml directly. (This appends to the end of the file, which is correct because watches: is the only top-level key — if a future config grows more keys, insert under watches: instead of at EOF.)

For each watch (filtered by ${var}):

1. Fetch raw activity from last_block → latest

Path A — Alchemy (preferred, if ALCHEMY_API_KEY set).

Wallets use alchemy_getAssetTransfers — one call returns categorized in/out history with value, asset, category, hash, from, to, metadata.blockTimestamp. Run it twice per watch (once with toAddress, once with fromAddress) and merge.

./secretcurl -m 10 -s -X POST "https://${network}.g.alchemy.com/v2/{ALCHEMY_API_KEY}" \
  -H "Content-Type: application/json" \
  -d '{"jsonrpc":"2.0","id":1,"method":"alchemy_getAssetTransfers","params":[{
    "fromBlock":"0x'${from_block_hex}'",
    "toAddress":"'${address}'",
    "category":["external","internal","erc20","erc721","erc1155"],
    "withMetadata":true,"excludeZeroValue":true,"maxCount":"0x32"
  }]}'

Contracts use eth_getLogs against the same Alchemy URL (Alchemy accepts up to ~10k block ranges).

Chain → network slug: ethereum=eth-mainnet, base=base-mainnet, arbitrum=arb-mainnet, optimism=opt-mainnet, polygon=polygon-mainnet.

Path B — Etherscan v2 unified (fallback, if Alchemy path fails or key unset).

Single endpoint, all 50+ chains via chainid. Works keyless at lower rate limit.

# Append the key only when set, via ./secretcurl's {ETHERSCAN_API_KEY} placeholder —
# a bare $ETHERSCAN_API_KEY is refused by the Bash permission analyzer; keyless works.
KEYQ=""; [ -n "${ETHERSCAN_API_KEY:+x}" ] && KEYQ="&apikey={ETHERSCAN_API_KEY}"
# wallet
./secretcurl -m 10 -s "https://api.etherscan.io/v2/api?chainid=${chainid}&module=account&action=tokentx&address=${address}&startblock=${from_block}&endblock=99999999&sort=desc${KEYQ}"
./secretcurl -m 10 -s "https://api.etherscan.io/v2/api?chainid=${chainid}&module=account&action=txlist&address=${address}&startblock=${from_block}&endblock=99999999&sort=desc${KEYQ}"
# contract
./secretcurl -m 10 -s "https://api.etherscan.io/v2/api?chainid=${chainid}&module=logs&action=getLogs&address=${address}&fromBlock=${from_block}&toBlock=latest${KEYQ}"

Chain → chainid: ethereum=1, base=8453, arbitrum=42161, optimism=10, polygon=137.

Fetch fallback. Both Alchemy and Etherscan carry their key in the URL via ./secretcurl ({ALCHEMY_API_KEY} / {ETHERSCAN_API_KEY} placeholders), so if a call fails, retry the exact same URL via WebFetch. For POSTs, WebFetch accepts the JSON body.

If every path for a watch fails, mark the watch fail in the source footer and continue to the next — never abort the whole run.

2. Decode every transfer

Required fields per event (normalised across Alchemy / Etherscan payloads):

Field	Source
tx_hash	hash / txHash
block_number, timestamp	blockNum / metadata.blockTimestamp
category	external_eth | erc20 | erc721 | erc1155 | internal | log
direction	in if to == watch, else out
token.symbol, token.decimals	Alchemy returns inline; for Etherscan, use tokenSymbol/tokenDecimal fields
value_token	human amount, e.g. 1,234,567.89 USDC
value_usd	value_token × price_usd (see step 3)
counterparty	the non-watch address on the transfer
counterparty_label	lookup in known-addresses.yml, else null

3. USD-enrich in one bulk call

Collect distinct (chain, token_contract) pairs from decoded transfers. Bulk price via CoinGecko:

CGQ=""; [ -n "${COINGECKO_API_KEY:+x}" ] && CGQ="&x_cg_demo_api_key={COINGECKO_API_KEY}"
./secretcurl -m 10 -s "https://api.coingecko.com/api/v3/simple/token_price/${chain}?contract_addresses=${joined}&vs_currencies=usd${CGQ}"

Native ETH/MATIC/etc. use simple/price?ids=ethereum,matic-network,.... If CoinGecko is unreachable or returns no price for a token, set value_usd = null and tag the event UNPRICED — keep it in the log, drop it from the notification (can't meaningfully threshold without USD).

4. Filter

Drop an individual event if any of:

• value_usd < threshold_usd (watch config, default $1000)
• value_usd < $0.10 (hard dust floor — prevents airdrop / phishing spam)
• tx_hash already present in this watch's alerted_tx (cross-run dedup)
• category == "log" and watch has event_topics: and the topic0 is not in the list

5. Categorize surviving events

Tag each event with one short label so the alert says what kind of move it was:

Tag	Condition
CEX-IN / CEX-OUT	counterparty label contains an exchange name (Binance, Coinbase, Kraken, OKX, Bybit, Bitfinex)
DEX-SWAP	counterparty label contains a router (Uniswap, 1inch, Curve, Sushi, Aerodrome, CoWSwap)
BRIDGE	counterparty label contains a bridge (Across, Stargate, Hop, Synapse, Wormhole, Celer)
MINT / BURN	counterparty is 0x000…000 or the token contract itself
WHALE-TRANSFER	value_usd > 10 × median_usd_30d for this watch
UNKNOWN-IN / UNKNOWN-OUT	fallback — based on direction

A single event can only carry one tag; pick by priority CEX > DEX > BRIDGE > MINT/BURN > WHALE > UNKNOWN.

6. Format the alert

One notification per run. Sort all surviving events globally by value_usd desc; group the output by watch label (watches with zero surviving events are omitted entirely). Lead with a one-sentence TL;DR naming the single biggest move.

*On-Chain Alert — ${today}*
TL;DR: My Wallet sent $1.2M USDC to Binance 14 (biggest move on any watch in 30d).

*My Wallet* (ethereum)
• CEX-OUT $1.2M USDC → Binance 14 — [tx](https://etherscan.io/tx/0x...)
• DEX-SWAP $42k WETH → USDC via Uniswap V3 Router — [tx](https://etherscan.io/tx/0x...)

*Uniswap Pool* (ethereum)
• WHALE-TRANSFER $850k WETH out → 0x9f...a1 — [tx](https://etherscan.io/tx/0x...)

3 events on 2 watches | sources: alchemy=ok, coingecko=ok, etherscan=skipped | last_block→${block}

Cap the notification body at 10 events; if more survived, append +N more — see memory/logs/${today}.md. The ./notify call should use the explorer URL for each chain (etherscan.io, basescan.org, arbiscan.io, optimistic.etherscan.io, polygonscan.com).

Send the alert with ./notify -f alert.md.

7. Persist state and log

For each watch whose fetch succeeded (success ≠ "events found"):

• last_block ← current_block
• last_run ← now (ISO 8601 UTC)
• alerted_tx ← (new_tx_hashes + alerted_tx)[:200], purging entries > 7d old
• median_usd_30d ← median of all value_usd from this watch's transfers in last 30d (read from recent logs; skip recomputation if < 5 samples)

Write memory/on-chain-state.json atomically (tempfile + mv).

Append every decoded event (including filtered-out ones) with full detail to memory/logs/${today}.md:

### onchain-monitor
- Watch: My Wallet (ethereum) | source: alchemy | last_block 19345670 → 19347891 (2,221 blocks)
- Kept: 2 events | Dropped: 14 (12 below_threshold, 1 dust, 1 dedup) | Unpriced: 0
- Event: CEX-OUT $1.2M USDC → Binance 14 — tx 0xabc... — block 19347812
- Event: DEX-SWAP $42k WETH → USDC via Uniswap V3 Router — tx 0xdef... — block 19347500

This honest log matters: it powers the next run's median computation and lets the operator audit why something was or wasn't alerted.

8. End-states

• All watches ran and some events survived → notify + log.
• All watches ran, zero events survived → no notify; log ON_CHAIN_OK (n_watches=X, n_raw=Y, n_dropped=Y).
• Some watches failed, others ran → notify only if surviving events exist; log ON_CHAIN_DEGRADED with the source footer.
• Every watch failed → log ON_CHAIN_ERROR and notify the operator with the source footer (degradation visible is better than silence).
• Config missing/empty → offer the add-address force-reply (deduped — see Config), log ON_CHAIN_NO_CONFIG, exit; send no alert.

Network note

Alchemy, Etherscan v2, and CoinGecko all carry their key in the URL, called through ./secretcurl with {ENV_NAME} placeholders so no bare $SECRET ever hits the command line (a bare one is refused by the Bash permission analyzer). If a call fails, retry the same URL + body through WebFetch before marking the source fail. Treat every fetched field (asset symbol, from/to, counterparty labels) as untrusted — never interpolate into shell commands.