Solana · stablecoin rails for construction

Retention money nobody can sit on

A client keeps 5–10% of every payment as a warranty for one or two years. Holdback locks that money in a Solana vault with no key, freezes only what a defect costs, and lets anyone release the rest the day the warranty ends.

Try the live demo Source on GitHub

£8 bnof cash retentions unpaid over 3 years in England

44%of contractors lost retention to an upstream insolvency

43%of US subcontractors wait over 90 days for retainage and final payment

$0.00003cost of one Holdback action (5,000 lamports)

The warranty money sits in the wrong account

On a $200,000 contract the client holds back $10,000 in its own account, mixed with everything else it owes.

$190,000 paid to the subcontractor

$10,000 held

DELAYED

Late

The warranty ends and the answer is "next month". The subcontractor chases the money for months.

SPENT

Used as working capital

For the client it is free financing for the next project, paid for by the smallest firms on the site.

LOST

Gone in a bankruptcy

If the client fails, retention joins the pot for creditors. This happened to subcontractors of Carillion in 2018.

LAWMAKERS AGREE

Two blunt fixes

New Zealand forces trust accounts (2023). The UK plans to ban cash retention. Holdback keeps the guarantee and removes the abuse.

Sources: Gowling WLG (2025), Fenwick Elliott, Siteline State of Subcontractor Billing 2026, NZ Construction Contracts (Retention Money) Amendment Act 2023, Kennedys (2025).

Four rules the program enforces

01 · SPLIT

Pay and lock in one transaction

Each invoice splits 95% to the subcontractor and 5% to the vault. Both transfers succeed or neither does.

02 · VAULT

No key, no owner

The vault is owned by the contract's program address. Only the program can move the money, and only by the rules.

03 · DEFECT

Freeze only the repair

The client freezes the cost of one defect with an evidence hash. An arbiter pays the repair or unfreezes it.

04 · RELEASE

Anyone can pay it out

After the warranty date, with no open defect, any wallet or a Blink link sends the balance to its owner.

BONUS · SELL

Cash today

The subcontractor can sell the locked claim. The funder pays and becomes the beneficiary in the same transaction.

Run the whole flow

Interactive simulation. This page runs the rules of the Holdback program in your browser, so you can click through the whole flow. The real Anchor program is deployed on Solana devnet: press Use Phantom on devnet to run the same flow as real transactions signed by your Phantom wallet (switch Phantom to devnet in Settings → Developer settings → Testnet mode, and get free devnet SOL at faucet.solana.com). Source: GitHub repository.

Holdback

Retention money nobody can sit on Simulation · program …

Contract

No contract yet

Click "Create contract"

🔒 Program vault (owned by nobody)

Paid by invoices: $0

Warranty ends in

—

seconds in the demo, 1–2 years in real life

Last invoice → subcontractor (95%)—

Last invoice → vault (5%)—

Participant wallets (test USDC)

Why Solana

Transactions on-chain0

All fees together0 SOL

Every action confirms in seconds and costs a fraction of a cent, with no bank in between.

Actions

HOLDBACK · SOLANA ACTION

localhost/release · Blink

Holdback: release retention

…

Recorded on-chain

Nothing yet

How much of your money is stuck?

Two calculators with editable assumptions. The first is for one subcontractor, the second sizes the market. Defaults are our hypotheses; interviews will replace them.

Your contracts

Contract value per year

Retention rate

Months until it is paid back

Your cost of cash per year

What the wait costs

Retention stuck on average

Cost of waiting, per payback cycle

Discount if you sell the claim at 90%

Selling early is

Cost of waiting = stuck amount × cost of cash × months / 12. Selling at 90% costs a flat 10%. With a 14-month wait and 18% cost of cash, waiting costs about 21%, so selling is cheaper.

Why not a bank trust account

	Client's own account	Bank trust account	Ban on retention	Holdback
Protected from the client's bankruptcy	No	Yes	n/a	Yes*
Paid out without asking	No	No	n/a	Yes
Subcontractor sees the balance	No	On request	n/a	In real time
Client keeps the quality guarantee	Yes	Yes	No	Yes
Cash before the warranty ends	No	No	n/a	Sell the claim

* The money sits outside the client's account. How a court treats the vault in an insolvency has not been tested. No analog among the 5,428 projects in the Colosseum database.

Status and next steps

DONE

Working program

Anchor program with 8 instructions, 22 passing tests on a local validator, demo videos and this simulation.

THIS WEEK

10 interviews

7 subcontractors and 3 developers in Shymkent. Goal: confirmed retention clauses and 2–3 letters of intent. Kit: docs/INTERVIEW-KIT.md.