ADR Format
ADRs live in docs/adr/ and use sequential numbering: 0001-slug.md, 0002-slug.md, etc.
Create the docs/adr/ directory lazily — only when the first ADR is needed.
Template
# {Short title of the decision}
{1-3 sentences: what's the context, what did we decide, and why.}That's it. An ADR can be a single paragraph. The value is in recording that a decision was made and why — not in filling out sections.
Optional sections
Only include these when they add genuine value. Most ADRs won't need them.
- Status frontmatter (
proposed | accepted | deprecated | superseded by ADR-NNNN) — useful when decisions are revisited - Considered Options — only when the rejected alternatives are worth remembering
- Consequences — only when non-obvious downstream effects need to be called out
Numbering
Scan docs/adr/ for the highest existing number and increment by one.
When to offer an ADR
All three of these must be true:
- Hard to reverse — the cost of changing your mind later is meaningful
- Surprising without context — a future reader will look at the code and wonder "why on earth did they do it this way?"
- The result of a real trade-off — there were genuine alternatives and you picked one for specific reasons
If a decision is easy to reverse, skip it — you'll just reverse it. If it's not surprising, nobody will wonder why. If there was no real alternative, there's nothing to record beyond "we did the obvious thing."
What qualifies
- Architectural shape. "We're using a monorepo." "The write model is event-sourced, the read model is projected into Postgres."
- Integration patterns between contexts. "Ordering and Billing communicate via domain events, not synchronous HTTP."
- Technology choices that carry lock-in. Database, message bus, auth provider, deployment target. Not every library — just the ones that would take a quarter to swap out.
- Boundary and scope decisions. "Customer data is owned by the Customer context; other contexts reference it by ID only." The explicit no-s are as valuable as the yes-s.
- Deliberate deviations from the obvious path. "We're using manual SQL instead of an ORM because X." Anything where a reasonable reader would assume the opposite. These stop the next engineer from "fixing" something that was deliberate.
- Constraints not visible in the code. "We can't use AWS because of compliance requirements." "Response times must be under 200ms because of the partner API contract."
- Rejected alternatives when the rejection is non-obvious. If you considered GraphQL and picked REST for subtle reasons, record it — otherwise someone will suggest GraphQL again in six months.