Milestone Escrow
The client locks the full budget up front, split into milestones. Funds move only on release, arbiter decision or cancellation.
Solidity 0.8.28OpenZeppelin v5ETH / ERC-20
SigmaNFT Collection
ERC-721 drop with Merkle allowlist, public phase, royalties and delayed reveal
ERC-721ERC-2981Merkle proofsFoundry
What it is
SigmaNFT stores only a Merkle root for the allowlist — users submit a proof, compatible with @openzeppelin/merkle-tree — so thousands of supporters can be allowlisted without writing addresses on-chain. Phases switch from Closed to Allowlist to Public, each with its own price and per-wallet cap, under a global, immutable maximum supply.
Until the owner reveals the collection, every token returns the placeholder metadata; after reveal it points to the final metadata. ERC-2981 royalties signal creator fees to marketplaces, and proceeds are withdrawn to the owner.
The business problem
An NFT drop must reward early supporters without storing thousands of addresses on-chain, stop bots and whales from sweeping the mint, earn royalties on secondary sales and prevent rarity sniping before the reveal. Naive implementations fail on exactly these points.
How it works
- 1
Off-chain: build a Merkle tree from the allowlist, publish the proofs and set the Merkle root.
- 2
The owner opens the allowlist phase; allowlisted wallets mint with their proof at the allowlist price.
- 3
The owner opens the public phase; anyone can mint up to the per-wallet cap.
- 4
After the mint, the metadata is uploaded to IPFS and the owner calls
reveal(baseURI). - 5
The owner withdraws the proceeds.
Security measures
- nonReentrant mint paths; counters updated before _safeMint callbacks
- Exact-payment rule — no refund logic, no lost ETH
- Double-hashed Merkle leaves verified with OpenZeppelin MerkleProof
- Immutable max supply; Ownable2Step
- Withdraw reverts instead of silently losing funds
- Fuzzed: supply ≤ MAX_SUPPLY, balance == minted × price
Features
- Merkle allowlist (proof-based)
- Closed → Allowlist → Public phases with separate prices
- Per-wallet limits per phase
- Immutable MAX_SUPPLY
- ERC-2981 royalties
- Delayed reveal
Typical use cases
- PFP and art drops, membership passes, event tickets
- Brand loyalty collections for existing customers
- Game item pre-sales with delayed rarity reveal
Known limitations
Metadata hosting (e.g. IPFS pinning) is operated off-chain.
Other showcase contracts
Token + Vesting + Staking
A capped ERC-20 with gasless approvals, vesting schedules with cliff for team and investors, and Synthetix-style staking rewards.
ERC-20EIP-2612OpenZeppelin v5
Gold-Backed Token (RWA)
Backing becomes a precondition of minting: tokens can only be minted if the reported gold reserve covers the new total supply.
ERC-20AccessControlProof of reserve
Standards: Solidity 0.8.x, OpenZeppelin, Foundry tests with fuzzing, Slither static analysis, verified source. 223 tests · 100% coverage · Slither-analysed.
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