Architecture Decision Records

Document significant technical decisions so future you (and your team) understands why choices were made.

When to Write an ADR

Write one when you're making a decision that:

Is hard to reverse later
Affects multiple parts of the system
Involves tradeoffs between valid options
Will be questioned by someone in 6 months

Examples: choosing a database, adopting a framework, changing auth strategy, restructuring the API, adding a build tool.

Template

Create files in docs/decisions/ (or adr/) with sequential numbering:

# ADR-001: Use PostgreSQL for primary database

## Status

Accepted | Proposed | Deprecated | Superseded by ADR-XXX

## Date

2026-04-10

## Context

What is the problem or situation that requires a decision?
Include constraints, requirements, and forces at play.

## Options Considered

### Option A: PostgreSQL
- Pros: ACID compliance, JSON support, mature ecosystem, free
- Cons: Requires managing connections, vertical scaling limits

### Option B: MongoDB
- Pros: Flexible schema, horizontal scaling
- Cons: No transactions across collections, eventual consistency issues

### Option C: PlanetScale (MySQL)
- Pros: Serverless, branching, managed
- Cons: Vendor lock-in, no foreign keys in their branching model

## Decision

We chose **PostgreSQL** because:
1. Our data is relational — users, teams, projects with clear relationships
2. We need ACID transactions for billing operations
3. JSON columns give us schema flexibility where needed
4. Prisma/Drizzle have excellent Postgres support

## Consequences

- We need to manage connection pooling (use PgBouncer or Prisma's built-in pool)
- Migrations must be backwards-compatible for zero-downtime deploys
- We accept vertical scaling limits and will shard later if needed

Workflow

Identify the decision being made
Research the options (at least 2-3 alternatives)
Write the ADR using the template
Review with the team (PR or discussion)
Merge as accepted
Reference from code comments when relevant: // See ADR-001

File Naming

docs/decisions/
├── 001-use-postgresql.md
├── 002-adopt-trpc-over-rest.md
├── 003-switch-to-pnpm.md
└── template.md

Tips

Keep ADRs short — 1-2 pages max
Write them in the present tense ("We choose X" not "We chose X")
It's OK to write an ADR after the fact if you forgot to write one during the decision
Superseded ADRs should link to their replacement, not be deleted
ADRs are not design docs — they capture the decision, not the full design

architecture-decision-records