What are Architecture Decision Records (ADRs)?
Architecture Decision Records (ADRs) are documents that capture important architectural decisions along with their context, consequences, and rationale. Each ADR documents a significant design choice—like adopting a microservices architecture, selecting a cloud provider, or choosing a technology stack—ensuring that critical knowledge persists as team members change and systems evolve. ADRs provide the technical foundation for maintaining consistent, maintainable architectures across time.
As a veteran software architect with decades of experience designing large-scale systems, I’ve found that documenting architectural decisions is one of the most critical activities in a project. Complex systems that evolve over many years cannot be properly maintained without understanding the rationale behind key design choices. This is where Architecture Decision Records, or ADRs, come into play.
An ADR is a document that captures an important architectural decision made along with its context and consequences. For example, we might have an ADR on adopting a microservices architecture, selecting a particular cloud provider, or choosing to rewrite a legacy subsystem. The goal is to explicitly articulate the motivations, alternatives considered, and implications of significant architectural decisions.
I recommend that every architect maintain a collection of ADRs for their system, stored alongside the codebase and updated continually as new decisions are made. Each ADR should include a concise title, the status (proposed, accepted, deprecated, etc), the context in which the decision arose, the actual decision made, and any important implications or additional details worth noting. Links to related ADRs are also helpful to understand interdependent choices.
The major benefit of ADRs is that they provide a technical record that persists across time as team members come and go. Without proper documentation, important context is lost and previous decisions are rehashed over and over. New engineers can get up to speed on system design much faster by consulting the set of ADRs. When encountering confusing or suboptimal code, tracing it back to the original ADR helps explain the situation. The ADR collection also aids future decision making by revealing constraints and trade-offs that were previously considered.
From a process perspective, I recommend reviewing ADRs regularly at architecture meetings and requiring sign-off from technical leads for impactful decisions. Lightweight ADRs can be created to explore potential ideas, while more durable ADRs capture commitments going forward. Versioning allows tracking of changes and helps communicate those changes to stakeholders. There are also tools emerging that facilitate ADR management as part of internal developer portals.
In essence, ADRs enable the kind of structured thinking and external documentation that is essential for consistent and maintainable architectures. As systems and organizations scale, it becomes untenable for architectural knowledge to remain trapped inside individual heads. I encourage all software teams to adopt the practice of architectural decision records for the long-term health of their critical systems. Let me know if you have any other questions!
Frequently Asked Questions
What should be included in an ADR?
Each ADR should include a concise title, status (proposed, accepted, deprecated, superseded), the context in which the decision arose, the actual decision made, and important implications or consequences. Additionally, include alternatives considered, trade-offs evaluated, and links to related ADRs to show interdependencies. The goal is to capture not just what was decided, but why it was decided and what impacts it has on the system.
How detailed should an ADR be?
ADRs should be detailed enough to capture the essential context and reasoning, but concise enough to be quickly readable. Most effective ADRs range from 200-500 words. The focus is on capturing the “why” rather than exhaustive technical documentation. Lightweight ADRs can be created for exploratory ideas, while more durable ADRs capture committed decisions. The right level of detail balances thoroughness with maintainability.
When should I create an ADR?
Create an ADR whenever making a significant architectural decision that will impact the system’s structure, behavior, or evolution. This includes technology choices, architectural patterns, system boundaries, data modeling approaches, and integration strategies. Not every decision requires an ADR—focus on decisions that are difficult to reverse, have broad impact, or would be confusing to future developers without context.
Where should ADRs be stored?
ADRs should be stored alongside your codebase in version control, typically in a dedicated /docs/adr/ directory. This ensures they evolve with the system and remain accessible to developers. Using markdown format keeps them simple and version-controllable. Some teams use specialized ADR tools that integrate with internal developer portals, but plain markdown files in git are often sufficient and more universally accessible.
How do ADRs differ from other documentation?
ADRs differ from technical specifications, requirements documents, and design documents in their focus. Specifications describe what to build, requirements describe desired capabilities, and design documents describe detailed implementation. ADRs specifically capture the architectural decisions behind these elements—the choices about system structure, technology selection, and design patterns that guide how requirements are implemented through detailed designs.
What is the status lifecycle of an ADR?
ADRs typically progress through statuses: Proposed (under consideration), Accepted (decision made and implemented), Deprecated (decision no longer recommended but still in use), and Superseded (replaced by a new decision, with link to the replacement ADR). This lifecycle helps teams track which decisions are current, which are historical, and how architectural thinking has evolved over time.
How do ADRs help with team onboarding?
ADRs dramatically accelerate onboarding by providing new engineers with immediate insight into the architectural rationale behind the system. Instead of wondering “why did they build it this way?”, new team members can consult the ADR collection to understand the context, constraints, and trade-offs that shaped the architecture. This reduces confusion, prevents rehashing of settled decisions, and helps new contributors work more effectively within established architectural patterns.
About the Author
Vinci Rufus is a software architect and writer with decades of experience designing large-scale systems. He writes about software architecture best practices, emerging development paradigms, and the documentation practices that enable teams to build maintainable systems. His work focuses on practical approaches to architectural decision-making and knowledge management in evolving codebases.