Vibecode Splitwise

You are building a lean indie version of Splitwise.

Create the following project files first, then implement the application by following them. Keep the files updated as decisions change. Do not collapse this into a single README or prompt.

===== README.md =====
# Splitwise indie build

## Goal

Build the smallest trustworthy replacement for the core Splitwise workflow for one developer or a tiny team.

## Scope

Create link-shared groups, log expenses with flexible splits, and settle up via minimum cash flow debt simplification.

## Quick start

1. Install the documented dependencies.
2. Copy `.env.example` to `.env`.
3. Run the development command chosen during implementation.
4. Complete the acceptance checks in `BUILD_PLAN.md`.

## Honest limits

This build deliberately does not replace:
- native iOS and Android apps, push reminders included
- your friends' existing accounts and muscle memory
- receipt scanning and itemized splits
- automatic currency conversion at live rates
- settle-up integrations with payment apps

If those capabilities are essential, use spliit instead of pretending the gap is solved.

===== AGENTS.md =====
# Agent instructions

- Optimize for a working, understandable weekend build.
- Prefer the fewest moving parts that satisfy the brief.
- Do not invent cryptography, security guarantees, APIs, or compliance claims.
- Keep secrets out of source control and logs.
- Add focused tests for destructive, security-sensitive, and data-loss paths.
- Run the project checks before declaring the build complete.
- Record any deliberate shortcut in the README under "Tradeoffs".

===== BUILD_PLAN.md =====
# Build plan

## Original build brief

Build a self-hosted group expense splitter: a single web app, no user accounts.

Stack: Node 22, Express, better-sqlite3, server-rendered EJS, htmx for interactivity. No build step, no SPA framework.

Features:
- Groups are created with one click and live at an unguessable URL (nanoid, 21 chars). The link is the auth model; say so plainly in the README.
- Members are names typed into the group, nothing more.
- Expenses: payer, amount, currency, date, note, category, and a split that can be equal, exact amounts, percentages, or shares.
- A balances view per group: each member's net position, plus a settle-up plan computed with minimum cash flow debt simplification.
- Reimbursements logged as a special expense type.
- Multi-currency: amounts stored in their own currency; a per-group manual rate table converts to the group's base currency. No external rate API.
- Edit and delete with a simple activity log.
- Export any group as CSV and JSON.

Storage: one SQLite file at ./data/app.db; path via .env. Ship a Dockerfile, a docker-compose.yml, and a README covering backups and reverse-proxy setup.

Out of scope, deliberately: accounts and OAuth, push notifications, receipt scanning, live exchange rates, payment integrations, native mobile apps. A PWA manifest so it installs to a home screen is the only concession.

## Required capabilities

- Implement the core workflow described in the build brief.

## Delivery order

1. Scaffold the smallest runnable application and document its commands.
2. Implement the primary data model and core workflow.
3. Add validation, safe failure states, and persistence.
4. Cover the critical path with automated tests.
5. Exercise a clean install from the README and fix every missing step.

## Done when

- A new user can go from clone to first successful workflow using only the README.
- The core workflow works without paid infrastructure unless the brief requires it.
- Tests cover the highest-risk behavior.
- Known limitations are explicit rather than hidden.

===== .env.example =====
# Copy to .env and document every variable when it is introduced.
# Never put real credentials in this file.

APP_ENV=development
# Add only values required by the selected implementation.

You are building a lean indie version of Splitwise.

Create the following project files first, then implement the application by following them. Keep the files updated as decisions change. Do not collapse this into a single README or prompt.

===== README.md =====
# Splitwise indie build

## Goal

Build the smallest trustworthy replacement for the core Splitwise workflow for one developer or a tiny team.

## Scope

Create link-shared groups, log expenses with flexible splits, and settle up via minimum cash flow debt simplification.

## Quick start

1. Install the documented dependencies.
2. Copy `.env.example` to `.env`.
3. Run the development command chosen during implementation.
4. Complete the acceptance checks in `BUILD_PLAN.md`.

## Honest limits

This build deliberately does not replace:
- native iOS and Android apps, push reminders included
- your friends' existing accounts and muscle memory
- receipt scanning and itemized splits
- automatic currency conversion at live rates
- settle-up integrations with payment apps

If those capabilities are essential, use spliit instead of pretending the gap is solved.

===== AGENTS.md =====
# Agent instructions

- Optimize for a working, understandable weekend build.
- Prefer the fewest moving parts that satisfy the brief.
- Do not invent cryptography, security guarantees, APIs, or compliance claims.
- Keep secrets out of source control and logs.
- Add focused tests for destructive, security-sensitive, and data-loss paths.
- Run the project checks before declaring the build complete.
- Record any deliberate shortcut in the README under "Tradeoffs".

===== BUILD_PLAN.md =====
# Build plan

## Original build brief

Build a self-hosted group expense splitter: a single web app, no user accounts.

Stack: Node 22, Express, better-sqlite3, server-rendered EJS, htmx for interactivity. No build step, no SPA framework.

Features:
- Groups are created with one click and live at an unguessable URL (nanoid, 21 chars). The link is the auth model; say so plainly in the README.
- Members are names typed into the group, nothing more.
- Expenses: payer, amount, currency, date, note, category, and a split that can be equal, exact amounts, percentages, or shares.
- A balances view per group: each member's net position, plus a settle-up plan computed with minimum cash flow debt simplification.
- Reimbursements logged as a special expense type.
- Multi-currency: amounts stored in their own currency; a per-group manual rate table converts to the group's base currency. No external rate API.
- Edit and delete with a simple activity log.
- Export any group as CSV and JSON.

Storage: one SQLite file at ./data/app.db; path via .env. Ship a Dockerfile, a docker-compose.yml, and a README covering backups and reverse-proxy setup.

Out of scope, deliberately: accounts and OAuth, push notifications, receipt scanning, live exchange rates, payment integrations, native mobile apps. A PWA manifest so it installs to a home screen is the only concession.

## Required capabilities

- Implement the core workflow described in the build brief.

## Delivery order

1. Scaffold the smallest runnable application and document its commands.
2. Implement the primary data model and core workflow.
3. Add validation, safe failure states, and persistence.
4. Cover the critical path with automated tests.
5. Exercise a clean install from the README and fix every missing step.

## Done when

- A new user can go from clone to first successful workflow using only the README.
- The core workflow works without paid infrastructure unless the brief requires it.
- Tests cover the highest-risk behavior.
- Known limitations are explicit rather than hidden.

===== .env.example =====
# Copy to .env and document every variable when it is introduced.
# Never put real credentials in this file.

APP_ENV=development
# Add only values required by the selected implementation.

You are building a production product version of Splitwise.

Create the following project files first, then implement the application by following them. Keep the files updated as decisions change. Do not collapse this into a single README or prompt.

===== PRODUCT.md =====
# Splitwise product brief

## Problem

The ledger and the debt math are a solved problem; a link-shared DIY version covers a household or one trip in a single sitting, no accounts needed. The gap is not code, it is adoption: Splitwise works because the whole group already has it installed, and nobody downloads your homebrew app for one weekend away. Build it for the people who share your fridge; for everyone else, the moat is other people's phones.

## Product outcome

Create link-shared groups, log expenses with flexible splits, and settle up via minimum cash flow debt simplification.

## Target user

A serious builder who needs a maintainable product foundation rather than a one-off demo.

## Required capabilities

- Implement the core workflow described in the build brief.

## Explicit non-goals for v1

- native iOS and Android apps, push reminders included
- your friends' existing accounts and muscle memory
- receipt scanning and itemized splits
- automatic currency conversion at live rates
- settle-up integrations with payment apps

## Success criteria

- The primary workflow is measurable end to end.
- Setup is reproducible in a clean environment.
- Failure, recovery, and support paths are documented.
- Product claims match what the implementation actually guarantees.

===== ARCHITECTURE.md =====
# Architecture

## Starting brief

Build a self-hosted group expense splitter: a single web app, no user accounts.

Stack: Node 22, Express, better-sqlite3, server-rendered EJS, htmx for interactivity. No build step, no SPA framework.

Features:
- Groups are created with one click and live at an unguessable URL (nanoid, 21 chars). The link is the auth model; say so plainly in the README.
- Members are names typed into the group, nothing more.
- Expenses: payer, amount, currency, date, note, category, and a split that can be equal, exact amounts, percentages, or shares.
- A balances view per group: each member's net position, plus a settle-up plan computed with minimum cash flow debt simplification.
- Reimbursements logged as a special expense type.
- Multi-currency: amounts stored in their own currency; a per-group manual rate table converts to the group's base currency. No external rate API.
- Edit and delete with a simple activity log.
- Export any group as CSV and JSON.

Storage: one SQLite file at ./data/app.db; path via .env. Ship a Dockerfile, a docker-compose.yml, and a README covering backups and reverse-proxy setup.

Out of scope, deliberately: accounts and OAuth, push notifications, receipt scanning, live exchange rates, payment integrations, native mobile apps. A PWA manifest so it installs to a home screen is the only concession.

## Boundaries

Separate the product into replaceable modules for interface, application logic, persistence, external integrations, and operational concerns. Keep domain logic independent from delivery frameworks and vendors.

## Production baseline

- Configuration: validated at startup with safe local defaults where possible.
- Security: least privilege, input validation, secret redaction, rate limits on abuse-prone paths, and no invented security primitives.
- Data: explicit schema and migrations, transactional writes where integrity matters, backup and restore instructions.
- Integrations: adapters around third-party providers, idempotent webhook or job processing, bounded retries, and timeouts.
- Observability: structured logs with request or operation IDs, an error-tracking hook, and health/readiness checks where a server exists.
- Quality: unit tests for domain rules, integration tests at module boundaries, and one end-to-end critical-path test.

## Decision records

For each major dependency, document why it was chosen, its failure mode, and how it can be replaced. Do not introduce infrastructure until a requirement justifies it.

===== AGENTS.md =====
# Agent instructions

- Read `PRODUCT.md` and `ARCHITECTURE.md` before changing code.
- Implement milestone by milestone; keep each change reviewable and leave the application runnable.
- Treat authentication, payments, encryption, imports, webhooks, and destructive actions as high-risk boundaries when present.
- Never invent cryptography or silently weaken a requirement to make a test pass.
- Use provider interfaces for external services and deterministic fakes in tests.
- Add migrations and rollback or recovery notes for persistent data changes.
- Log useful operational context without credentials, tokens, passwords, or personal data.
- Update documentation and run all checks before completing a milestone.

===== MILESTONES.md =====
# Delivery milestones

## M0 — Decisions and scaffold

- Confirm the runtime, persistence model, threat boundaries, and deployment target.
- Create a reproducible local environment and continuous checks.

## M1 — Core workflow

- Implement the smallest end-to-end product path with validation and tests.
- Keep integrations behind interfaces.

## M2 — Trust layer

- Add secure failure behavior, recovery paths, audit-relevant events, and data safeguards.
- Test abuse cases and destructive operations.

## M3 — Operability

- Add structured logs, error reporting hooks, health signals, backup/restore documentation, and deployment configuration.

## M4 — Release gate

- Run a clean-install test, critical-path end-to-end test, dependency review, and documented rollback exercise.
- Compare the shipped behavior with `PRODUCT.md` and publish remaining limitations.

===== OPERATIONS.md =====
# Operations

## Before release

- Validate configuration and secrets at startup.
- Define backup, restore, and rollback procedures and test them.
- Document logs, error tracking, health signals, and alert ownership.
- Set dependency update and vulnerability review expectations.

## Incident checklist

1. Contain the issue without destroying evidence or user data.
2. Record the timeline and affected scope.
3. Rotate exposed secrets and revoke compromised sessions or credentials.
4. Restore from a verified source when needed.
5. Document the root cause, remediation, and regression test.

## Launch constraint

Do not market omitted Splitwise capabilities as implemented. The v1 non-goals in `PRODUCT.md` remain user-visible limitations until they are deliberately delivered.

# Splitwise indie build

## Goal

Build the smallest trustworthy replacement for the core Splitwise workflow for one developer or a tiny team.

## Scope

Create link-shared groups, log expenses with flexible splits, and settle up via minimum cash flow debt simplification.

## Quick start

1. Install the documented dependencies.
2. Copy `.env.example` to `.env`.
3. Run the development command chosen during implementation.
4. Complete the acceptance checks in `BUILD_PLAN.md`.

## Honest limits

This build deliberately does not replace:
- native iOS and Android apps, push reminders included
- your friends' existing accounts and muscle memory
- receipt scanning and itemized splits
- automatic currency conversion at live rates
- settle-up integrations with payment apps

If those capabilities are essential, use spliit instead of pretending the gap is solved.

# Agent instructions

- Optimize for a working, understandable weekend build.
- Prefer the fewest moving parts that satisfy the brief.
- Do not invent cryptography, security guarantees, APIs, or compliance claims.
- Keep secrets out of source control and logs.
- Add focused tests for destructive, security-sensitive, and data-loss paths.
- Run the project checks before declaring the build complete.
- Record any deliberate shortcut in the README under "Tradeoffs".

# Build plan

## Original build brief

Build a self-hosted group expense splitter: a single web app, no user accounts.

Stack: Node 22, Express, better-sqlite3, server-rendered EJS, htmx for interactivity. No build step, no SPA framework.

Features:
- Groups are created with one click and live at an unguessable URL (nanoid, 21 chars). The link is the auth model; say so plainly in the README.
- Members are names typed into the group, nothing more.
- Expenses: payer, amount, currency, date, note, category, and a split that can be equal, exact amounts, percentages, or shares.
- A balances view per group: each member's net position, plus a settle-up plan computed with minimum cash flow debt simplification.
- Reimbursements logged as a special expense type.
- Multi-currency: amounts stored in their own currency; a per-group manual rate table converts to the group's base currency. No external rate API.
- Edit and delete with a simple activity log.
- Export any group as CSV and JSON.

Storage: one SQLite file at ./data/app.db; path via .env. Ship a Dockerfile, a docker-compose.yml, and a README covering backups and reverse-proxy setup.

Out of scope, deliberately: accounts and OAuth, push notifications, receipt scanning, live exchange rates, payment integrations, native mobile apps. A PWA manifest so it installs to a home screen is the only concession.

## Required capabilities

- Implement the core workflow described in the build brief.

## Delivery order

1. Scaffold the smallest runnable application and document its commands.
2. Implement the primary data model and core workflow.
3. Add validation, safe failure states, and persistence.
4. Cover the critical path with automated tests.
5. Exercise a clean install from the README and fix every missing step.

## Done when

- A new user can go from clone to first successful workflow using only the README.
- The core workflow works without paid infrastructure unless the brief requires it.
- Tests cover the highest-risk behavior.
- Known limitations are explicit rather than hidden.

# Copy to .env and document every variable when it is introduced.
# Never put real credentials in this file.

APP_ENV=development
# Add only values required by the selected implementation.

# Splitwise product brief

## Problem

The ledger and the debt math are a solved problem; a link-shared DIY version covers a household or one trip in a single sitting, no accounts needed. The gap is not code, it is adoption: Splitwise works because the whole group already has it installed, and nobody downloads your homebrew app for one weekend away. Build it for the people who share your fridge; for everyone else, the moat is other people's phones.

## Product outcome

Create link-shared groups, log expenses with flexible splits, and settle up via minimum cash flow debt simplification.

## Target user

A serious builder who needs a maintainable product foundation rather than a one-off demo.

## Required capabilities

- Implement the core workflow described in the build brief.

## Explicit non-goals for v1

- native iOS and Android apps, push reminders included
- your friends' existing accounts and muscle memory
- receipt scanning and itemized splits
- automatic currency conversion at live rates
- settle-up integrations with payment apps

## Success criteria

- The primary workflow is measurable end to end.
- Setup is reproducible in a clean environment.
- Failure, recovery, and support paths are documented.
- Product claims match what the implementation actually guarantees.

# Architecture

## Starting brief

Build a self-hosted group expense splitter: a single web app, no user accounts.

Stack: Node 22, Express, better-sqlite3, server-rendered EJS, htmx for interactivity. No build step, no SPA framework.

Features:
- Groups are created with one click and live at an unguessable URL (nanoid, 21 chars). The link is the auth model; say so plainly in the README.
- Members are names typed into the group, nothing more.
- Expenses: payer, amount, currency, date, note, category, and a split that can be equal, exact amounts, percentages, or shares.
- A balances view per group: each member's net position, plus a settle-up plan computed with minimum cash flow debt simplification.
- Reimbursements logged as a special expense type.
- Multi-currency: amounts stored in their own currency; a per-group manual rate table converts to the group's base currency. No external rate API.
- Edit and delete with a simple activity log.
- Export any group as CSV and JSON.

Storage: one SQLite file at ./data/app.db; path via .env. Ship a Dockerfile, a docker-compose.yml, and a README covering backups and reverse-proxy setup.

Out of scope, deliberately: accounts and OAuth, push notifications, receipt scanning, live exchange rates, payment integrations, native mobile apps. A PWA manifest so it installs to a home screen is the only concession.

## Boundaries

Separate the product into replaceable modules for interface, application logic, persistence, external integrations, and operational concerns. Keep domain logic independent from delivery frameworks and vendors.

## Production baseline

- Configuration: validated at startup with safe local defaults where possible.
- Security: least privilege, input validation, secret redaction, rate limits on abuse-prone paths, and no invented security primitives.
- Data: explicit schema and migrations, transactional writes where integrity matters, backup and restore instructions.
- Integrations: adapters around third-party providers, idempotent webhook or job processing, bounded retries, and timeouts.
- Observability: structured logs with request or operation IDs, an error-tracking hook, and health/readiness checks where a server exists.
- Quality: unit tests for domain rules, integration tests at module boundaries, and one end-to-end critical-path test.

## Decision records

For each major dependency, document why it was chosen, its failure mode, and how it can be replaced. Do not introduce infrastructure until a requirement justifies it.

# Agent instructions

- Read `PRODUCT.md` and `ARCHITECTURE.md` before changing code.
- Implement milestone by milestone; keep each change reviewable and leave the application runnable.
- Treat authentication, payments, encryption, imports, webhooks, and destructive actions as high-risk boundaries when present.
- Never invent cryptography or silently weaken a requirement to make a test pass.
- Use provider interfaces for external services and deterministic fakes in tests.
- Add migrations and rollback or recovery notes for persistent data changes.
- Log useful operational context without credentials, tokens, passwords, or personal data.
- Update documentation and run all checks before completing a milestone.

# Delivery milestones

## M0 — Decisions and scaffold

- Confirm the runtime, persistence model, threat boundaries, and deployment target.
- Create a reproducible local environment and continuous checks.

## M1 — Core workflow

- Implement the smallest end-to-end product path with validation and tests.
- Keep integrations behind interfaces.

## M2 — Trust layer

- Add secure failure behavior, recovery paths, audit-relevant events, and data safeguards.
- Test abuse cases and destructive operations.

## M3 — Operability

- Add structured logs, error reporting hooks, health signals, backup/restore documentation, and deployment configuration.

## M4 — Release gate

- Run a clean-install test, critical-path end-to-end test, dependency review, and documented rollback exercise.
- Compare the shipped behavior with `PRODUCT.md` and publish remaining limitations.

# Operations

## Before release

- Validate configuration and secrets at startup.
- Define backup, restore, and rollback procedures and test them.
- Document logs, error tracking, health signals, and alert ownership.
- Set dependency update and vulnerability review expectations.

## Incident checklist

1. Contain the issue without destroying evidence or user data.
2. Record the timeline and affected scope.
3. Rotate exposed secrets and revoke compromised sessions or credentials.
4. Restore from a verified source when needed.
5. Document the root cause, remediation, and regression test.

## Launch constraint

Do not market omitted Splitwise capabilities as implemented. The v1 non-goals in `PRODUCT.md` remain user-visible limitations until they are deliberately delivered.

$ choose a build depth, inspect the files, then open the complete pack in your agent