multiflow open-sources the iframe rate calculator

multiflow today open-sourced its iframe rate calculator under the MIT license, making the widget available to any operator — not just multiflow customers — who wants to embed a payments rate-quote tool on their own site. The repository includes the full frontend, a Node.js reference backend, worked examples, and theming documentation.

"We had a choice," said a multiflow engineering lead. "Keep the calculator as a customer-only feature, or ship it under MIT and let the whole operator community benefit. The calculator is not the product — the underwriting relationships, the acquirer stack, and the orchestration layer are the product. The calculator is just a nice front-end, and the operator ecosystem is better off if anyone can use it."

The decision aligns with a broader pattern multiflow has followed since launch: calculators, templates, and reference documents are free. The commercial offering is the actual orchestration layer. Operators who want to use multiflow's calculator without ever opening a multiflow account can now do so legally, with no attribution or backlink requirement.

What's in the repository

The open-source release includes everything needed to run the calculator from scratch:

• Frontend widget. Single-file iframe with responsive CSS and the same three-input flow (vertical, volume, ticket size) multiflow ships to operators.
• Reference backend. Node.js server returning the rate quote based on configurable interchange assumptions. Operators plug in their own interchange cost structure.
• Theming docs. Full CSS override guide plus a small set of pre-built themes (dark, light, neutral, brand-matched).
• Vertical configuration. YAML file defining rate-card logic per vertical. Forks can add or remove verticals without touching code.
• Compliance mode. Optional regulatory disclosure text for CA/NY, matching multiflow's internal compliance mode.
• Tests. 146 unit tests covering rate logic, edge cases, and theming.

What the open-source version does NOT include

Three things stay inside multiflow's customer-only product: (1) the live interchange feed that drives multiflow's internal quotes — the open-source version uses a published interchange table that operators update manually; (2) the short-lived token auth system that binds the widget to an operator portal; (3) the direct-to-underwriting lead routing that pushes completed quotes into multiflow's underwriting pipeline. Operators running the open-source version get the frontend and the math; they do not get the underwriting layer.

That distinction is intentional. The front-end calculator is a commodity; the underwriting is not.

Why MIT, not something stricter

multiflow picked MIT specifically because it is the most permissive commonly-used open-source license. Operators can fork the repository, white-label the widget, embed it on commercial sites, and never once mention multiflow. There is no copyleft obligation to share modifications back, no attribution requirement, and no use restriction.

"We thought about Apache or BSD," said the engineering lead. "MIT is shorter, more widely understood, and operators don't need to lawyer-read it. That's the right call for a front-end widget."

Contribution model

multiflow will continue to maintain the canonical upstream repository and will merge contributions via standard pull request flow. The internal multiflow version — which is a superset of the open-source version — will continue to be developed, and improvements that are appropriate to share back (accessibility, performance, bug fixes, new verticals) will be merged upstream on a monthly cadence.

Operators who find bugs, want new verticals supported, or want to contribute a new theme can open an issue or PR on the public repository. The repository includes a contribution guide and a code of conduct.

Comparison to existing operator-facing calculators

The calculator joins multiflow's existing collection of operator tools, including:

• Effective rate calculator for multi-brand
• Interchange-plus breakdown calculator
• Reserve cost calculator
• PCI scope estimator
• MATCH-list escape timeline tool
• Chargeback ratio calculator

The iframe rate calculator is the first of multiflow's tools to be formally open-sourced. If adoption goes well — measured by fork count, issue quality, and operator feedback — multiflow will move the other calculators to MIT in phases through 2026.

Who should use the open-source version

Three operator profiles:

1. Non-multiflow operators who want a functional rate-quote tool on their own site and are willing to maintain their own interchange feed.
2. Agencies and consultancies that build operator sites for clients and want a reusable calculator component.
3. Payments-adjacent tool builders who want to embed rate-quote functionality in a larger product (CRM, finance dashboard, etc).

About multiflow

multiflow is the operator-first payment orchestration layer for multi-brand e-commerce portfolios. Built for operators running 3-42 brands, multiflow consolidates acquirer relationships, descriptor management, reserve negotiation, and reconciliation into a single operator-facing surface. Pricing is volume-tiered, 5.5-7.5% per transaction plus a one-time setup fee, with interchange passed through. The iframe rate calculator is now MIT-licensed and available on GitHub; the commercial multiflow offering is at the pricing page.