Writing Down Architecture Decisions So the Reasoning Doesn't Get Lost

A useful record captures four things briefly: the specific problem being solved, the options that were genuinely considered, the decision made, and the consequences accepted as a tradeoff, including the downsides of the chosen option that were knowingly accepted rather than missed. That last part is the piece teams skip most often, and it's the piece that matters most a year later, since it tells a future reader the current pain point was already known about, not an oversight.

Keep each record short enough to read in a couple of minutes, a page at most for the vast majority of decisions. A record that takes thirty minutes to read gets skipped by the person who actually needs the context during an urgent debugging session, which is exactly the moment this document is supposed to help.

A useful record covers four points, briefly:

• The specific problem being solved, stated so a future reader understands it without extra context.
• The options that were genuinely considered, not only the one that won.
• The decision made, stated plainly so nobody has to guess what was chosen.
• The consequences accepted as a tradeoff, including downsides of the chosen option that were knowingly accepted rather than missed.

Not every technical choice needs a formal record; a record for every minor implementation detail produces noise that buries the decisions that actually matter under trivial ones. A reasonable bar is whether the decision would be expensive to reverse, whether reasonable engineers could disagree about the right call, or whether the reasoning depends on constraints, a deadline, a team's size at the time, a vendor limitation, that won't be obvious to someone reading the code alone months or years later.

A schema design choice for a core data model, a decision to build versus buy a piece of infrastructure, a choice of messaging pattern for a critical pipeline: these clear the bar. A choice of variable naming convention or a minor library version pin generally doesn't.

A decision record buried in a wiki separate from the code it describes tends to go stale and unfound, since engineers working in the code have no natural prompt to go looking for it. Store records in the same repository as the code they describe, in a consistent, predictable location, so they show up naturally in a pull request diff or a directory listing rather than requiring someone to remember a separate system exists.

Link to the relevant record directly from code comments at the specific point the decision affects, not just from a central index. A comment reading see the decision record for why this uses polling instead of a webhook gives a future engineer the context exactly where and when they need it, rather than relying on them to already know to search for it.

A decision record process that depends on one enthusiastic engineer remembering to write them up dies the day that engineer moves to a different team or leaves. Build it into an existing habit instead, a required section in your pull request template for changes above a certain size, or a standing agenda item in architecture review meetings, so writing the record is a natural byproduct of a process that already exists rather than an extra optional step.

Revisit old records periodically, not to rewrite history, but to add a note when a decision's context has changed or the tradeoff accepted at the time is no longer the right one. A record marked as superseded, with a link to what replaced it and why, is far more useful to a future reader than a stale document that reads as current but describes a decision nobody actually follows anymore.