SUBway

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  Landing Page

LINK TO THE PROJECT

https://subway3.jachammer.app/

Inspiration

Developers often keep paying for unused subscriptions because they cannot answer one critical question: “What will break if I downgrade this?” We built SUBway to make subscription management safer and more actionable.

What it does

SUBway connects GitHub, Supabase, and OpenAI to map projects, services, and subscriptions as a dependency graph. It identifies potential savings, explains their impact, and can execute and verify approved Supabase actions.

We started with Supabase and OpenAI because their APIs support usage analysis and actionable cost optimization. The same approach can expand to other developer platforms.

How we built it

We built the entire application in Jac. Walkers scan GitHub manifests, detect service usage, construct the dependency graph, and generate deterministic recommendations. Jac’s by llm() explains each recommendation, while provider APIs handle execution and verification.

Challenges we ran into

The hardest challenge was connecting repository dependencies, provider resources, usage, and costs into one reliable model. We also had to handle inconsistent API data, protect against unsafe actions, and verify that provider changes actually completed.

Accomplishments that we're proud of

We created an end-to-end workflow that discovers dependencies automatically, finds savings, explains the risks, requests approval, executes an action, and verifies the result. We are also proud that the full stack, including the interface, is written in Jac.

What we learned

We learned that subscription optimization is not just a billing problem. It is a dependency problem. Usage data becomes much more valuable when it is connected to the projects and services it supports.

What's next for SUBway

Next, we plan to add AWS, Vercel, GitHub seats, monitoring tools, rollback support, scheduled scans, team approvals, and policies that protect production resources.

Built With

• jac
• jachammer
• noriaki
• steven