Constitutional Fee Protocol (Demo)

A minimal, forkable reference implementation of a “constitutional” protocol fee that decreases automatically with global protocol volume, enforced in code.

This repository is intended to be a starting point for discussion and experimentation (e.g. on ethresear.ch), not a production-ready fundraising or payments system.

You can read the Motivation for this project

And the Engineering Perspecive is here

What this is

• A Solidity fee model where the protocol fee is a deterministic function of global trailing volume.
• The fee is bounded:
  • starts at f_max
  • decays with adoption (global volume)
  • approaches a non-zero floor f_min for sustainability
• A minimal ERC20 “donation intake” contract demonstrating how the fee would be applied, with an auditable event log.

Fee function (alpha = 1 power-law)

Let V be trailing global protocol volume (e.g., trailing 90 days), and V0 be a scale parameter.

f(V) = f_min + (f_max - f_min) * V0 / (V0 + V)

This is the α=1 special case of:

f(V)=f_min + (f_max-f_min)/ (1+V/V0)^alpha

…and is “logarithmic” in the sense that the log of the excess fee is linear in log(1 + V/V0).

What this is not

• No token.
• No DAO.
• No yield.
• No governance knobs for fees in this demo.
• No claim this solves compliance, KYC, fraud, or payout rails (e.g. M-PAiSA) — those are separate layers.

Repository layout

• contracts/
  • FeeModel.sol – pure fee math (BPS + power-law decay)
  • ConstitutionalFeeOracle.sol – immutable parameters and fee computation
  • DonationIntake.sol – sample intake applying the fee
  • MockGlobalVolumeOracle.sol – testing-only oracle (mutable; not constitutional)
• test/ – Hardhat tests
• scripts/ – example deployment script

Quick start

Prerequisites

• Node.js 18+ (or 20+)
• npm

Install

npm install

Compile

npm run build

Test

npm test

Design notes

“Global trailing volume” oracle

A real system needs a robust definition of V (trailing volume), and a credible way to compute it.

This demo includes MockGlobalVolumeOracle so tests and examples work. In production, you would replace it with something like:

• on-chain rolling volume buckets (if all flows are on-chain), or
• attested aggregates from payment/payout adapters (if many flows originate off-chain), with clear constitutional rules for exclusions (refunds, reversals, wash volume).

Credible neutrality & enforcement

The purpose of this approach is to make fee extraction:

• transparent
• bounded
• predictable
• difficult to quietly change

In a live protocol, hard forks (social consensus) are the enforcement mechanism if the constitution must change.

License

MIT. See LICENSE.

Disclaimer

This code is provided for educational and research discussion purposes only. It has not been audited and is not intended for production use.