finops-architect-toolkit

After years reviewing architectures in financial environments, the cloud bill always reached my desk before it reached finance. The reason is simple: architecture choices — instance type, storage class, Lambda memory, tag granularity — settle most of the invoice before any discount contract is signed. The question that shows up in the meeting isn't "how much does it cost?" — it's "what do we optimize first, and with what evidence?".

The problem is that this conversation happens in three dialects. Procurement talks about commitment, term and discount. Engineering talks about invocations, GB-seconds and storage class. Finance talks about cost center and allocation. I was spending too long translating between them in spreadsheets, and every spreadsheet died at the end of the meeting.

What this toolkit solves: putting the four calculations that repeat most — Reserved Instance break-even, S3 class transition, monthly Lambda cost by dimension and the tag schema that supports allocation — in one place, in one language, so the discussion starts at the trade-off and not at the arithmetic.

What it is not: a replacement for Cost Explorer, the Cost and Usage Report or the AWS Pricing API. The numbers that go into the calculators are your assumptions; the tool does the comparison and shows where the tipping point sits. Treat every result as an argument for a conversation, not as an invoice reconciliation.

The application is a Next.js 16 frontend with React 19, TypeScript 5 and Tailwind CSS 4, living under frontend/. Each calculator is a screen: you enter your assumptions, the screen returns the comparison and the tipping point. There is no backend of its own and no AWS credential involved — which makes the tool safe to open in front of a client or paste into a meeting link without exposing any account.

Pipeline: three GitHub Actions workflows look after the repository — ci (typecheck and build), frontend and security. Deployment goes to Vercel, DNS sits on Cloudflare, and the published version runs at finops.moretes.com. docs/architecture.md describes the structure; OPERATIONS.md and SETUP.md cover operations and environment setup.

What each calculator answers:

• RI vs On-Demand answers "from what utilization does the commitment pay off?". If the instance runs fewer hours per month than the break-even indicates, the discount becomes a loss.
• S3 answers "at what retrieval cost do I switch class?". Glacier and Deep Archive are only cheap for objects nobody reads; the first bulk restore gives the difference back.
• Lambda answers "memory or duration — which dimension do I attack?". Doubling memory usually cuts duration; the calculator shows whether the balance closes.
• Tagging answers "which keys do I require before any resource goes up?". A tag added later is rework across the whole account.

Honest limit: prices are user input. Region, instance type and tier change the unit value — check the Pricing Calculator or the Pricing API before signing anything based on a number generated here.