modbender Ceaser Privacy Protocol
You are a skill that interacts with the Ceaser privacy protocol on Base L2 (chain ID 8453). Ceaser lets users shield (deposit) ETH into a privacy pool and unshield (withdraw) to any address, using zero-knowledge proofs. No trusted setup -- the protocol uses Noir circuits compiled to UltraHonk proofs.
Base URL: https://ceaser.org
All endpoints below are public and require no authentication. Rate limits: 60 req/min (read), 5 req/min (write) per IP.
For a complete OpenAPI 3.0 specification, see {baseDir}/references/openapi.json.
Read-Only Queries
List valid denominations with fee breakdown
Shows what amounts users can shield/unshield and the exact costs (0.25% protocol fee).
curl -s "https://ceaser.org/api/ceaser/denominations" | jq .
Valid denominations: 0.001, 0.01, 0.1, 1, 10, 100 ETH.
Calculate fee breakdown for a specific amount
curl -s "https://ceaser.org/api/ceaser/fees/100000000000000000" | jq .
The amount parameter is in wei. 100000000000000000 = 0.1 ETH. Response includes protocolFee (0.25%), treasuryShare (0.24%), relayerAlloc (0.01%), and netAmount.
Get pool statistics
curl -s "https://ceaser.org/api/ceaser/pool/0" | jq .
Asset ID 0 = ETH. Returns totalLocked (TVL in wei), totalLockedFormatted (human readable), totalNotes, and feeBps.
Get current Merkle root
curl -s "https://ceaser.org/api/ceaser/merkle-root" | jq .
Returns the 24-level Poseidon Merkle tree root. The source field indicates whether it came from the local indexer (instant) or fell back to an on-chain query.
Check if a nullifier has been spent
curl -s "https://ceaser.org/api/ceaser/nullifier/0x0000000000000000000000000000000000000000000000000000000000000001" | jq .
Replace the hash with the actual bytes32 nullifier hash. Returns { "spent": true/false }.
Facilitator health and status
curl -s "https://ceaser.org/status" | jq .
Returns facilitator wallet balance, registered protocols, circuit breaker state, transaction queue info, persistent transaction tracker stats, and indexer sync status.
Simple liveness check
curl -s "https://ceaser.org/health" | jq .
Returns { "ok": true } if the facilitator is running.
Indexer Queries
The indexer maintains a local Merkle tree synchronized with the on-chain contract. It provides instant access to commitments and root data without RPC calls.
Indexer sync status
curl -s "https://ceaser.org/api/ceaser/indexer/status" | jq .
Returns synced, syncInProgress, lastSyncBlock, leafCount, root, and operational stats.
Indexed Merkle root (instant, no RPC)
curl -s "https://ceaser.org/api/ceaser/indexer/root" | jq .
List commitments (paginated)
curl -s "https://ceaser.org/api/ceaser/indexer/commitments?offset=0&limit=100" | jq .
Returns commitments array, total count, offset, and limit. Max 1000 per page.
Get commitment by leaf index
curl -s "https://ceaser.org/api/ceaser/indexer/commitment/0" | jq .
x402 Facilitator (Gasless Settlement)
The facilitator is a gasless relay: it validates ZK proofs and submits them on-chain, paying gas on behalf of the user. This enables withdrawals from wallets with zero ETH balance.
x402 capability discovery
curl -s "https://ceaser.org/supported" | jq .
Returns supported schemes (zk-relay), networks (eip155:8453), protocols (ceaser), and proof formats (ultrahonk).
Verify a ZK proof (dry run, no on-chain submission)
curl -s -X POST "https://ceaser.org/verify" \
-H "Content-Type: application/json" \
-d '{
"protocol": "ceaser",
"network": "eip155:8453",
"payload": {
"proof": "0x...",
"nullifierHash": "0x...",
"amount": "100000000000000000",
"assetId": "0",
"recipient": "0x742d35Cc6634C0532925a3b844Bc9e7595f2bD18",
"root": "0x..."
}
}' | jq .
Returns isValid, validation details, gas estimate, and facilitator fee.
Submit ZK proof on-chain (gasless settlement)
curl -s -X POST "https://ceaser.org/settle" \
-H "Content-Type: application/json" \
-d '{
"protocol": "ceaser",
"network": "eip155:8453",
"payload": {
"proof": "0x...",
"nullifierHash": "0x...",
"amount": "100000000000000000",
"assetId": "0",
"recipient": "0x742d35Cc6634C0532925a3b844Bc9e7595f2bD18",
"root": "0x..."
}
}' | jq .
The facilitator pays gas. Recipient receives amount minus 0.25% protocol fee. Idempotent: resubmitting the same nullifier returns the cached result.
Prepare a Shield Transaction
This builds an unsigned transaction for shielding ETH. The user must sign and submit it from their own wallet.
curl -s -X POST "https://ceaser.org/api/ceaser/shield/prepare" \
-H "Content-Type: application/json" \
-d '{
"proof": "0x...",
"commitment": "0x...",
"amount": "100000000000000000",
"assetId": "0"
}' | jq .
Returns pre-built transaction data (to, data, value) and fee breakdown. The caller signs this with their wallet.
IMPORTANT: Shield operations require generating a ZK proof client-side. The proof, commitment, and secret/nullifier must be generated using the Ceaser frontend (https://ceaser.org) or the ceaser-mcp npm package (npx ceaser-mcp). This skill cannot generate proofs -- it only queries the API.
CLI Subcommands (Shield / Unshield)
The ceaser-mcp npm package includes CLI subcommands that run directly from bash. These generate ZK proofs locally and interact with the facilitator for gasless settlement. All output is JSON.
Shield ETH (generate proof + unsigned tx)
npx -y ceaser-mcp shield 0.001
Returns an unsigned transaction (to, data, value) and a note backup string. The user must sign and send the transaction from their wallet. Valid denominations: 0.001, 0.01, 0.1, 1, 10, 100 ETH.
IMPORTANT: The backup field in the output contains the note's private keys. It MUST be saved securely -- it is the only way to later unshield the funds.
List stored notes
npx -y ceaser-mcp notes
Shows unspent notes with their IDs, amounts, and leaf indices. Add --all to include spent notes.
Unshield ETH (gasless withdrawal via x402)
npx -y ceaser-mcp unshield <noteId> 0x742d35Cc6634C0532925a3b844Bc9e7595f2bD18
Generates a burn ZK proof and submits it to the facilitator. The facilitator pays gas. The recipient receives the amount minus 0.25% protocol fee. Requires a stored note with a valid leaf index (shield tx must have confirmed on-chain).
Import a note from backup
npx -y ceaser-mcp import eyJzIjoiMTIzLi4uIn0=
Imports a note from a base64 backup string (generated by shield or the Ceaser frontend). Required before unshielding a note created elsewhere.
Help
npx -y ceaser-mcp help
Notes are stored at ~/.ceaser-mcp/notes.json. All commands output JSON to stdout on success and JSON to stderr on failure.
Key Concepts
- Shield: Deposit ETH into the privacy pool. Creates a note (commitment) on-chain. Requires ZK proof generation (client-side only).
- Unshield: Withdraw ETH from the privacy pool to any address. Requires a stored note with secret/nullifier. The facilitator handles gas.
- Note: A private record containing secret, nullifier, amount, and commitment. Notes are never stored on-chain -- only their Poseidon hash (commitment) is.
- Nullifier: A unique identifier derived from the note. Once spent, the nullifier is recorded on-chain to prevent double-spending.
- Denomination: Fixed amounts (0.001 to 100 ETH) to prevent amount-based deanonymization.
- Protocol Fee: 0.25% (25 basis points) split between treasury (0.24%) and relayer fund (0.01%).
Performing Transactions (Shield / Unshield)
When a user asks to shield or unshield ETH, use one of these options:
Option 1: CLI subcommands (recommended for agents)
Use the CLI subcommands documented above. This is the fastest path for bash-capable agents:
# Shield
npx -y ceaser-mcp shield 0.001
# List notes to get noteId
npx -y ceaser-mcp notes
# Unshield
npx -y ceaser-mcp unshield <noteId> <recipient>
The shield command generates a ZK proof locally and returns an unsigned transaction. The user must sign and send it. The unshield command generates a burn proof and settles via the facilitator (gasless).
Option 2: Web App (non-technical users)
Direct the user to https://ceaser.org -- connect wallet, select amount, click Shield or Unshield. The frontend handles proof generation, wallet signing, and note management in-browser.
Option 3: MCP Server via Claude Code
The ceaser-mcp npm package also runs as an MCP server for Claude Code:
claude mcp add --transport stdio ceaser -- npx -y ceaser-mcp
This provides 10 MCP tools including ceaser_shield_eth and ceaser_unshield. Notes are stored locally at ~/.ceaser-mcp/notes.json.
npm package: https://www.npmjs.com/package/ceaser-mcp
What this skill can help with
While you wait for a transaction or are exploring the protocol, this skill can:
- Check denominations and fees before shielding
- Monitor pool TVL and note count
- Verify a nullifier is unspent before attempting unshield
- Check facilitator health and circuit breaker state
- Browse indexed commitments and Merkle tree state