The challenge
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Case Study
ContaMCP
Track income, expenses, budgets, and savings in ChatGPT.
An open-source finance tracker that keeps your records available across chats. The service is live; its public ChatGPT plugin is awaiting review.
ChatGPTContaMCP connected
Why ContaMCP exists
The approach
Record transactions and ask questions in chat. Conta saves your entries and calculates the totals.
Key features
ChatGPTContaMCP connected
ContaMCP
ContaMCP
ContaMCP
01
Income and expense tracking
Say "Record 125.50 MXN for groceries today." Your assistant can ask for missing details before saving, and you can retrieve the entry in a new chat.
ChatGPTContaMCP connected
I spent $45 on gas today.
Used ContaMCP
Done, your expense has been recorded.
- Expense: Gas
- Amount: $45.00 USD
- Category: Transport
- Date:
Want to see how much you’ve spent on transport this month?
ContaMCP
Record the expense from this receipt.
Used ContaMCP
Done, your expense has been recorded.
- Expense: Gas
- Amount: $45.00 USD
- Category: Transport
- Date:
Want to see how much you’ve spent on transport this month?
ContaMCP
I got paid $4,200 today. Log it as salary.
Used ContaMCP
Done, your income has been recorded.
Salary ·
+$4,200.00 USD
Your month so far
| This month | USD |
|---|---|
| Income | +$4,200.00 |
| Expenses | −$1,044.99 |
| Recorded balance | +$3,155.01 |
Want a breakdown of your income this month?
ContaMCP
02
See where your money goes
Ask how much you spent this month or which categories cost the most. Get totals from your saved records, with MXN, USD, and EUR kept separate.
ChatGPTContaMCP connected
How much did I spend this month?
Used ContaMCP
Here’s your spending so far this month:
Total spent this month
$1,044.99 USD
From the start of the month through today
Spending by category
- Food & drinks$420.00
- Transport$185.00
- Groceries$360.00
- Utilities$79.99
Want to compare your spending with last month?
ContaMCP
I got paid $4,200 today. Log it as salary.
Used ContaMCP
Done, your income has been recorded.
Salary ·
+$4,200.00 USD
Your month so far
| This month | USD |
|---|---|
| Income | +$4,200.00 |
| Expenses | −$1,044.99 |
| Recorded balance | +$3,155.01 |
Want a breakdown of your income this month?
ContaMCP
03
Find ways to save
Ask where you could cut back. Your assistant can review spending by category, suggest a target for next month, and show how much you could save.
ChatGPTContaMCP connected
Where could I cut back on spending?
Used ContaMCP
Based on your recorded expenses, here’s one place to start:
Start with food & drinks
This is your largest recorded spending category this month. Review those expenses for changes that fit your routine.
- Spent this month
- $420.00 USD
- Suggested target for next month
- $350.00 USD
Less spending if you meet that target$70.00 USD
Want to set a food budget for next month?
ContaMCP
04
Recurring entries, budgets, and goals
Set up recurring income and expenses, monthly budgets, and savings goals. Scheduled entries are saved when due and stay unverified until you confirm payment. Conta does not move money.
ChatGPTContaMCP connected
What recurring payments do I have coming up?
Used ContaMCP
Here are your upcoming recorded recurring payments:
Upcoming payments
- MusicMonthly$10.99 USD
- RentMonthly$1,400.00 USD
- InternetMonthly$59.99 USD
Want to see the details of a payment?
ContaMCP
How are my savings for the trip coming along?
Used ContaMCP
Here’s your progress toward the trip:
Trip to Lisbon
In two months$1,200.00of $3,000.00 USD
Want to record a contribution?
ContaMCP
What I built
A finance tracker with saved records, sign-in, recurring entries, and exports, connected to ChatGPT through MCP tools.
Agent / MCP Integration
- Built typed tools for recording income and expenses, reports, recurring entries, budgets, savings, and exports.
- Kept domain rules independent of the assistant and transport, with structured results and clear failure responses.
- Tested financial workflows and safe failures in ChatGPT on desktop, then verified saved-entry retrieval on a phone.
Platform / Systems
- Deployed a TypeScript service on Cloudflare Workers, with Hono, Drizzle, D1 / SQLite, and KV.
- Used integer minor units for money, owner-scoped persistence, version checks, audit history, and idempotent retries.
- Integrated Google sign-in and scoped OAuth grants with PKCE, plus isolated staging and production configuration.
Open Source / Self-hosting
- Published the source under the MIT license with setup, security, operations, and contribution documentation.
- Offered a hosted service so people can sign in with Google and connect their assistant.
- Added deployment guides for developers who want to run their own instance.
Engineering decisions
The choices that keep records accurate when people manage their finances through chat.
Keep records outside the chat
ChatGPT handles the conversation. ContaMCP stores each entry and calculates totals, so a new chat can retrieve the same records.
Check changes and keep their history
Check account ownership before every change. Version checks catch conflicting edits, retry keys prevent repeated requests from creating duplicate entries, and corrections keep their history.
Support hosted use and self-hosting
People can sign in with Google and use the hosted service. Developers can inspect the MIT-licensed source and follow the guides to run their own instance.