adr-documentation

ADR Documentation

Overview

What are ADRs?

Architecture Decision Records (ADRs) are lightweight documents that capture important architectural decisions along with their context and consequences. They serve as a historical record of why certain choices were made, helping teams avoid revisiting settled debates and providing context for future developers.

Key characteristics:

• Immutable: Once accepted, ADRs are rarely modified (supersede instead)
• Context-rich: Capture the environment and constraints at decision time
• Outcome-focused: Document what was decided and why
• Alternative-aware: Show what options were considered and rejected

Why Document Decisions?

Context Preservation:

• Future team members understand why things are the way they are
• Avoid "we've always done it this way" without knowing the reason
• Preserve institutional knowledge across team changes

Onboarding:

• New developers can read ADR history to understand system evolution
• Reduces repetitive explanations of architectural choices
• Provides learning path through project decisions

Avoiding Repeat Mistakes:

• Document why certain approaches were rejected
• Prevent re-proposing failed solutions
• Learn from past trade-offs

Alignment:

• Create shared understanding across team
• Resolve disagreements with documented rationale
• Enable asynchronous decision-making

When to Write an ADR

Write an ADR when:

• Significant architectural choices: Microservices vs monolith, event-driven vs request/response
• Technology selections: Database choice, framework adoption, language decisions
• Pattern decisions: State management approach, authentication strategy, error handling patterns
• Breaking changes: API redesigns, data model changes, migration strategies
• Performance-critical decisions: Caching strategies, optimization approaches, scalability patterns
• Security-related choices: Authentication methods, encryption strategies, access control models
• Infrastructure decisions: Deployment strategy, hosting platform, CI/CD approach
• Dependency selections: Major library choices, third-party service integrations

Don't write an ADR for:

• Minor implementation details
• Temporary workarounds
• Personal coding style preferences
• Reversible low-impact choices

ADR Structure

Standard Format

# ADR-XXXX: [Short Title]

## Status
[Proposed | Accepted | Deprecated | Superseded by ADR-YYYY]

## Date
YYYY-MM-DD

## Context
[Problem statement and environment]

## Decision
[What was decided]

## Consequences
[What results from this decision]

## Alternatives Considered
[Other options evaluated]

## Related ADRs
[Links to related decisions]

## References
[External links and documentation]

Section Guidelines

Title:

• Format: ADR-XXXX: Short Decision Title
• Be specific: "ADR-0012: Use PostgreSQL for Primary Database"
• Not generic: "ADR-0012: Database Choice"

Status:

• Proposed: Under discussion, not yet accepted
• Accepted: Decision is final and being implemented
• Deprecated: No longer recommended but not replaced
• Superseded by ADR-YYYY: Replaced by a newer decision

Date:

• Use ISO format: YYYY-MM-DD
• Date of status change, not original proposal

Context:

• Describe the forces at play
• Technical constraints
• Business requirements
• Team capabilities
• Timeline pressures
• Budget considerations
• Example: "We need to store structured data with complex relationships. Team has limited database expertise. Must support 100k+ users within 6 months."

Decision:

• State clearly what was decided
• Include scope and boundaries
• Specify what is NOT included
• Example: "We will use PostgreSQL as our primary database for all structured data. NoSQL solutions may be used for specific use cases (caching, session storage) but PostgreSQL is the default."

Consequences:

• Positive: What benefits we gain
• Negative: What drawbacks we accept
• Neutral: What trade-offs we're making

Example:

### Positive
- Strong ACID guarantees for transactions
- Rich query capabilities with SQL
- Mature ecosystem and tooling

### Negative
- Requires careful index management for performance
- Scaling horizontally is more complex than NoSQL
- Team needs PostgreSQL training

### Neutral
- Need to establish backup/restore procedures
- Must define connection pooling strategy

Alternatives Considered:

• List 2-4 alternatives seriously evaluated
• For each: Pros, Cons, Why rejected
• Be fair to alternatives (avoid strawman arguments)

Related ADRs:

• Link to decisions that influenced this one
• Link to decisions this one influences
• Create a decision graph over time

References:

• Documentation links
• Blog posts or articles that influenced decision
• Benchmark results
• Proof of concepts

ADR Numbering and Naming

Sequential Numbering

Use zero-padded sequential numbers:

• ADR-0001, ADR-0002, ..., ADR-0010, ..., ADR-0100
• Four digits handles up to 9,999 ADRs (enough for most projects)
• Don't skip numbers when superseding (new ADR gets next number)

File Naming

Format: ADR-XXXX-short-title.md

Examples:

• ADR-0001-use-postgresql-database.md
• ADR-0002-adopt-react-19-frontend.md
• ADR-0003-implement-jwt-authentication.md

Naming guidelines:

• Use lowercase
• Use hyphens (not underscores or spaces)
• Keep title short but descriptive
• Include key technology/pattern name

Location

Recommended locations:

• Option 1: ai-docs/decisions/ (alongside other AI-focused docs)
• Option 2: docs/adr/ (standard documentation location)
• Option 3: Root adr/ directory (if ADRs are primary docs)

Choose consistently across project.

For Claude Code plugins:

• Use ai-docs/decisions/ to co-locate with CLAUDE.md and other AI docs
• Makes ADRs easily discoverable by Claude

When to Write an ADR

Technology Adoption

Write an ADR when:

• Adopting a new framework or major library
• Choosing between competing technologies
• Upgrading to a new major version with breaking changes

Examples:

• ADR-0015: Migrate from Webpack to Vite
• ADR-0023: Adopt TypeScript for Backend Services
• ADR-0031: Use Bun Runtime Instead of Node.js

Architectural Pattern Selection

Write an ADR when:

• Choosing architectural style (monolith, microservices, serverless)
• Selecting state management approach
• Defining API design patterns
• Establishing error handling strategies

Examples:

• ADR-0008: Use Event-Driven Architecture for Order Processing
• ADR-0012: Implement Repository Pattern for Data Access
• ADR-0019: Adopt REST over GraphQL for Public API

Breaking Changes

Write an ADR when:

• Making changes that break backward compatibility
• Migrating data models
• Redesigning core APIs
• Changing authentication mechanisms

Examples:

• ADR-0025: Remove Legacy API v1 Endpoints
• ADR-0033: Migrate from Sessions to JWT Tokens
• ADR-0041: Change User ID from Integer to UUID

Performance-Critical Decisions

Write an ADR when:

• Implementing caching strategies
• Making database optimization choices
• Selecting algorithms for hot paths
• Deciding on async vs sync processing

Examples:

• ADR-0017: Implement Redis for Session Caching
• ADR-0022: Use WebSockets for Real-Time Updates
• ADR-0028: Adopt Background Job Queue for Heavy Processing

Security-Related Choices

Write an ADR when:

• Choosing authentication methods
• Implementing authorization strategies
• Selecting encryption approaches
• Defining security policies

Examples:

• ADR-0010: Use OAuth 2.0 with PKCE for Mobile Auth
• ADR-0014: Implement Row-Level Security in PostgreSQL
• ADR-0020: Adopt OWASP Guidelines for API Security

ADR Lifecycle

Proposal Phase

Creating a Proposal:

1. Draft ADR with status "Proposed"
2. Share with team for feedback
3. Discuss in team meeting or async comments
4. Iterate on Context and Alternatives sections

Review Process:

• Ensure all alternatives are fairly represented
• Verify consequences are realistic
• Check that context captures current constraints
• Validate decision aligns with project goals

Acceptance

When to Accept:

• Team consensus reached (or decision maker approves)
• Decision is being implemented
• No major unresolved concerns

Accepting an ADR:

1. Change status to "Accepted"
2. Update date to acceptance date
3. Commit to repository
4. Communicate to team

Post-Acceptance:

• ADR becomes immutable (don't edit decision or alternatives)
• May add notes or references sections if new info emerges
• Use comments to clarify, don't rewrite history

Deprecation Process

When to Deprecate:

• Decision is no longer recommended but not replaced
• Technology or pattern is obsolete
• Security vulnerability makes approach unsafe

Deprecating an ADR:

1. Change status to "Deprecated"
2. Add "Deprecation Note" section explaining why
3. Update date to deprecation date
4. Don't remove ADR from repository

Example deprecation note:

## Deprecation Note (2026-01-15)

This decision has been deprecated due to security vulnerabilities
discovered in the XYZ library. See ADR-0045 for the replacement
approach using the ABC library.

Superseding Old ADRs

When to Supersede:

• Making a decision that replaces an old one
• Reversing a previous decision
• Evolving a decision with significant changes

Superseding Process:

1. Create new ADR with next sequential number
2. Reference old ADR in "Context" section
3. Update old ADR status to "Superseded by ADR-XXXX"
4. Explain why old decision is being replaced

Example: Old ADR-0012:

## Status
Superseded by ADR-0034

New ADR-0034:

## Context
ADR-0012 chose MongoDB for our primary database. After 2 years
of production use, we've encountered scaling issues with our
relational data model. This ADR supersedes

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