Project Track 6: Automated Expense & Tax Analyst

The Problem / Concept A financial tool that turns messy physical receipts into structured data and checks them against personal budget rules.

Project Overview & Objectives

Freelancers and small business owners lose hours manually entering receipts and figuring out tax deduction rules. This application automates the ingestion of physical financial documents and strictly categorizes them according to local tax laws and personal budget constraints.

If you select this track, your goal is to build a functional Minimum Viable Prototype (MVP) that seamlessly integrates a Node.js/Express backend with Google’s Gemini API, utilizing Retrieval-Augmented Generation (RAG), multimodal vision, and autonomous tool calling.

Detailed Requirements Document (PRD)

1. RAG (Obsidian) Core Requirement

To prevent hallucination, the AI must be grounded in a specific, personal knowledge base. You will build this using Markdown files in Obsidian.

  • Knowledge Base Content: The exocortex contains the user’s monthly budget allocations (e.g., ‘Dining: $300’), a list of tax-deductible categories specific to their freelance profession, and previous monthly spending summaries to provide comparative context.
  • Implementation Expectation: Your Express server must parse these Markdown files, generate vector embeddings using gemini-embedding-2, and perform a cosine similarity search against the user’s query. The retrieved text must be injected into the system prompt.

2. Multimodal (Vision) Stretch Goal

AI is not just text. Modern products must perceive the world.

  • Vision Use Case: Users upload photos of crumpled physical receipts, handwritten taxi invoices, or screenshots of digital payments. The model extracts the Vendor Name, Date, Line Items, and Total Amount, structuring it perfectly into JSON.
  • Implementation Expectation: Your frontend HTML must include a file upload input. The image must be converted to base64, sent to the /query endpoint, and passed to gemini-2.5-flash alongside the text prompt and RAG context.

3. Tool Calling Stretch Goal

Agents need to take actions in the real world or fetch real-time data that isn’t in their RAG database.

  • Tool Definition: Implement an export_to_sheets(json_data) tool. The AI can be instructed to trigger this tool to push the extracted and categorized receipt data directly into a mock Google Sheets database.
  • Implementation Expectation: You must define a strict JSON schema for this tool and register it in your Gemini API call. When the model decides to invoke the tool, your Node.js server must intercept the request, execute a mock function, and return the result to the model for the final response.

Step-by-Step Implementation Guide

If you are using this document to prompt an AI coding assistant (like GitHub Copilot or Cursor), use the following phasing:

  1. Phase 1: UI & Mock Backend: Ask the AI to generate a vanilla HTML/JS interface with a text input, file upload, and a submit button. Connect it to an Express POST /query route that returns mock JSON.
  2. Phase 2: Vanilla Gemini Integration: Connect the Express route to the actual @google/genai SDK. Send a simple text prompt and display the result.
  3. Phase 3: The RAG Pipeline: Ask the AI to write a script to read your Markdown files, split them into chunks, and get embeddings. Update your /query route to calculate cosine similarity and inject the top matches.
  4. Phase 4: Multimodal & Tools: Finally, add the base64 image parsing to the API call, and define your function declaration for the tool-calling stretch goal.

Starter branch & solutions

You are on Track 6: Automated Expense & Tax Analyst.

First-time setup

git clone https://github.com/arjankc/ai-product-engineering.git
cd ai-product-engineering
git fetch --tags
git checkout track-06
cp .env.example .env
# Session 7+: paste GEMINI_API_KEY into .env (never commit .env)
npm install
npm run dev

Equivalent full branch name: track-06-automated-expense-tax-analyst (use this if you need to commit and a short tag left you in detached HEAD).

This track ships a PRD README, ~7–8 domain seed notes in sample-vault/, and a lightly branded starter UI. Expand the vault toward ≥10 notes before showcase. Stay on your track for graded work — do not submit from main or a solution tag.

Open http://localhost:3000.

If you already cloned the repo

cd ai-product-engineering
git fetch --tags
git checkout track-06
npm install
npm run dev

When stuck (public step-by-step solutions)

Build on your track first. When blocked—or after the lab hour—open the matching phase tag, diff, learn, then return:

git fetch --tags
git checkout solution-06-phase-1   # Sessions 5–6 — UI & mock
# git checkout solution-06-phase-2   # Session 7 — Gemini
# git checkout solution-06-phase-3   # Sessions 8–9 — real RAG + sources
# git checkout solution-06-phase-4   # Sessions 10–12 — multimodal, safety, tools
git checkout track-06              # return and keep building

Phase 4 includes calculator + search_knowledge_base plus this track’s domain tool: export_to_sheets. Tip tag solution-06 is showcase reference only — not a drop-in submission.

Guides: BRANCHES.md · HOW-TO-USE-SOLUTIONS.md · GATES.md.