BlocksMaples: a P2P crypto marketplace with USDT escrow
The whole product: API, web app and iOS/Android app, in English, Korean and Chinese.
Read the buildBlockchain and dApp development, from contract to app
We build smart contracts and the product around them: the backend that indexes the chain, the web and mobile apps people use, and the admin tools your team runs it from.
Talk to an engineer, not a salesperson.
5.0 out of 5 starsClient ratings
Founder's certification: Hedera Developer (The Hashgraph Association, 2026)
BC-01Chain = Index of the chain
IllustrationThe problem
The contract is the smallest part
Users judge a blockchain product on the parts that aren't on-chain: how fast it loads, whether the balance is right, and whether a pending transaction is shown honestly. The contract is often the smallest part of the work.
Every serious on-chain product is really two systems that must agree: the chain, and the index of the chain. Teams that treat indexing as a detail find the gap during a reorg, an RPC outage or a restart. Usually it shows up as data that is quietly wrong rather than visibly broken.
What we build
The contract, and everything that has to agree with it.
Smart contract development (EVM, Hedera)
Smart contracts for EVM chains, and token and messaging services on Hedera. Upgrade strategy and admin rights are decided before deployment, not after a bug.
Indexing and read APIs
An indexer turns chain events into tables your app can query quickly. It is built to survive reorgs, restarts and RPC gaps without counting anything twice.
RPC resilience
More than one node provider, with failover. It is designed so a failover can't submit the same transaction twice.
Reconciliation
Your backend's balances are compared with the chain continuously. A mismatch raises an alert instead of drifting.
Wallets and transaction state
Connection, signing and status handled so the interface never shows a pending transaction as done. Pending, confirmed and failed look different.
Testing
Contract tests, integration tests against a forked chain, and tests for the failure paths, not only the happy one.
Evidence
Proof from client work
A client's review, the case studies, and our recent blockchain jobs with their dates.
“Excellent freelancer. The work was completed professionally and showed strong understanding of modern web application design, SaaS-style presentation, user experience, and secure system interface requirements…”
Recent blockchain work
| When | Project type | Engagement | Rating |
|---|---|---|---|
| Jul–Sep 2026 | Website and blockchain build | Fixed price | 5.0 out of 5 stars |
| Jun–Jul 2026 | Web-based blockchain OTC platform | Fixed price | 5.0 out of 5 stars |
| Jun 2026 | Blockchain voting and SaaS pricing design | Fixed price | 5.0 out of 5 stars |
| May 2026 | Election feature for an existing web app | Fixed price | 5.0 out of 5 stars |
| Oct 2025–May 2026 | Blockchain developer, long-term | Hourly · 106 h | No feedback given |
Ratings, reviews and engagement dates come from client contracts delivered through Upwork, checked 24 Sep 2026. '…' marks where a quote was shortened. Client names stay private.
dApps
NFT marketplace development
Minting, listing, transfers and royalties live on-chain. The hard parts are usually off-chain: search, media storage, and keeping listings in step with the chain so a sold item never shows as available.
- Media on IPFS, with a pinning plan someone actually maintains.
- Royalty and fee logic decided per chain before deployment.
dApps
OTC and P2P trading platforms
A P2P or OTC venue is an escrow and dispute system with a trading screen attached. We scope it that way: who holds funds and when, how deposits are verified, how withdrawals are approved, and what an admin sees in a dispute.
For BlocksMaples we built a P2P marketplace settled in USDT on BNB Smart Chain, with web and iOS/Android apps. The internet-facing API holds no signing keys. An isolated worker signs withdrawals, and deposits are re-verified on-chain before they're credited.
- Escrow rules: when funds lock, who can release them, and what happens when one side goes quiet.
- Deposits credited from the chain's own record, not from a webhook alone.
- Withdrawal limits, one-time codes and a signing service kept off the public API.
Detail
Deposit credit reads the amount from the chain, after enough confirmations, never from the webhook payload.
dApps
Blockchain voting systems
A voting system has to do three things at once: one person gets one vote, the result can be checked, and ordinary voters can use it. We've built voting and election features in two fixed-price client jobs, one of them on an existing app's login and database.
- Eligibility and one-vote rules enforced on the server, and on-chain where that adds trust.
- Results people can verify, with an audit trail for disputes.
For companies
Enterprise blockchain: Hyperledger and IoT
For a company, a blockchain is usually infrastructure: a shared record several parties can trust, or a tamper-evident log of data from devices in the field. Permissioned does not mean private. It means identified, so the identity model is the design.
- Hyperledger Fabric networks with endorsement policies that match how your organisations actually work.
- Device data signed at a gateway and anchored to a ledger as hashes, with the raw data kept off-chain.
Anupam's advisory work includes Hyperledger Fabric on ARM64 edge devices, with architecture and security reports.
We don't hold SOC 2 or ISO 27001.
Hedera
Hedera development (HTS, HCS)
Hedera has built-in services for tokens (HTS) and for ordered, timestamped messages (HCS), alongside EVM smart contracts. Many token and audit-log products can use those services directly, with no custom contract to write, audit or upgrade.
Founder's certification
Hedera Developer Certification · The Hashgraph Association · May 2026
Process
How a blockchain project runs
Four steps. You get something you can read at the end of each.
Discover
We decide what must be on-chain, what only needs to be verifiable, and who holds which keys.
You get
A written brief.
Architect
Contract design, upgrade path, admin rights, the indexer and the trust boundary, written down before code.
You get
An architecture doc, the key decisions (ADRs) and a milestone plan with estimates.
Build
Contracts, indexer, backend and apps in small increments, on a testnet first.
You get
Regular demos and written updates.
Validate and hand over
Failure-path tests, a forked-chain run and UAT. For anything holding real value, we recommend an independent audit before mainnet and prepare the code for it.
You get
UAT sign-off and handover notes.
Pricing
How pricing works
A paid discovery sprint, then fixed-price milestones. Ongoing work can run on a dedicated engineer by the month.
What changes the price
The number of contracts and chains, whether the product holds user funds, the integrations, and your audit timeline. An independent audit is contracted and paid separately, with the auditor.
- Discovery sprint
- Fixed-price milestones
- Dedicated engineer, monthly
- Hourly
Start here
Launching a contract or dApp soon?
Web3 readiness check
An 11-point check before you launch a contract or dApp. Results on screen; no email needed.
Questions
Questions we get about blockchain work
Do you audit smart contracts?
We do internal security review and write tests against known failure classes. For a system holding meaningful value, we recommend a specialist third-party audit as well. Our review is engineering diligence, not a substitute for a formal audit.
Which chains do you work on?
EVM chains, Solana, Hedera, and permissioned networks.
How do you handle chain reorgs?
The indexer treats confirmations as probabilistic until a finality threshold, and projections are written so they can be rolled back and reapplied. The interface shows pending and confirmed as genuinely different states.
Three ways to start
Planning a blockchain or dApp build?
Pick whichever suits you. A person reads every message.