A new engineer asks why the product uses a particular database or deployment arrangement. The team remembers that the choice was discussed, but the reasoning is scattered across old messages.
Without that context, a reasonable early decision can look arbitrary. The team may repeat the original debate or preserve a temporary compromise long after its purpose has disappeared.
An architecture decision record, or ADR, provides a compact place to preserve the decision and the circumstances that shaped it.
Record a decision worth revisiting
Not every implementation detail needs an ADR.
Focus on choices that materially affect how the product is built, operated, or changed. Examples might include a major service boundary, a shared data model, or a deployment approach.
AWS’s guidance identifies recurring problems such as decisions made without recorded justification and decisions that are forgotten because they were never captured. ADRs preserve the context and considerations for current and future team members.
The value comes from preserving reasoning that would otherwise be expensive to reconstruct.
Describe the constraints that actually existed
For a hypothetical startup, an early architecture choice might reflect a small engineering team, limited operational experience, and a narrow initial workload.
Write those conditions explicitly.
“The team selected this approach because it could operate it with the available staff” explains more than “This approach is simpler.”
Include meaningful alternatives and why they were not selected. Avoid turning the record into a retrospective sales pitch for the chosen option.
A future reader needs to understand the tradeoffs, including the disadvantages the team knowingly accepted.
Keep the structure short and recognizable
The UK Government Digital Service describes an ADR structure containing a title, status, context, decision, and consequences. Its guidance explicitly includes both positive and negative consequences.
A useful title states the decision.
“Use one deployment unit for the initial service” is more informative than “Architecture discussion.”
The consequences section should identify what becomes easier and what may become harder. For example, a choice could simplify deployment while making independent scaling less convenient.
Keep supporting diagrams or measurements linked where needed, rather than duplicating an entire architecture document inside every record.
Distinguish acceptance from implementation
A team can agree to a design before the necessary work has been completed.
Track that implementation separately so an accepted decision is not mistaken for a description of the current system.
For a hypothetical migration, the ADR might explain the destination and rationale, while the issue tracker records the remaining changes.
Review the record if implementation reveals a previously unknown constraint.
The documentation should help readers distinguish intention, current behavior, and historical reasoning.
Preserve the history when the decision changes
GDS recommends storing architecture decisions in version control and marking superseded decisions clearly, with links to their replacements.
For a startup, this makes changing direction easier to explain.
A later decision can state that the workload, staffing, or product requirements have changed. The original record remains useful evidence of why the earlier approach was reasonable.
Add a review trigger where helpful, such as a particular operational problem or expansion in scope. This invites reconsideration based on evidence rather than fashion.
An ADR is successful when a future teammate can understand the choice without finding everyone who attended the original discussion. A short, candid record can preserve that understanding as the company grows.
Sources: Sources: AWS: Architectural decision records · GDS: Documenting architecture decisions