Keep a decision log beside the PRD

A PRD can be perfectly clear about what to build and still leave the team unable to explain why. That gap appears later, when a constraint changes or someone asks to revisit a trade-off. The document has requirements, but the reasoning that produced them is scattered across meetings, chat, and memory.

I treat a decision log as a small companion to the spec. It is not meeting minutes and it is not a place to defend every choice forever. Its job is to make important choices legible enough that the team can execute them now and reconsider them intelligently later.

Capture choices, not conversation#

A meeting transcript records what was said. A decision log records what the team will do, and the boundary around that commitment. The distinction matters because discussion often contains tentative ideas that never become decisions.

For example, imagine a team deciding how a document-review tool should handle an unreadable upload. The transcript might include several possible responses: ask for a clearer file, try a second extraction method, or let a person review it. The log should say which behavior ships first, why, and what happens when it fails. It should not preserve every suggestion as though it were still under consideration.

A useful entry can fit in a few lines:

The table is a prompt, not paperwork to complete for every tiny detail. Use it for choices that affect user outcomes, architecture, scope, risk, or dependencies. If a decision can be reversed in minutes and has no meaningful knock-on effects, recording it may cost more than it saves.

Keep evidence separate from assumptions#

A rationale becomes brittle when opinion is presented as fact. Write down what is known, what is inferred, and what remains uncertain. That lets someone update the decision without having to reject the entire argument.

Suppose a team chooses not to support a certain file format in the first release. The evidence might be that the current parser cannot reliably extract its contents. The assumption might be that few target users need it. The decision could be to show a clear unsupported-format message rather than silently accepting the file. Those are three different statements, and they age at different speeds.

A practical template is:

Evidence: what we observed or can verify. Assumption: what we believe but have not established. Choice: what we will do given both. Revisit when: what signal would change the balance.

Avoid vague rationales such as “best UX,” “industry standard,” or “engineering prefers it.” Replace them with the actual trade-off: “We will ask for a replacement file rather than return a partial summary, because a partial result could be mistaken for complete coverage.” That sentence makes the user risk visible and gives a future reviewer something specific to test.

Do not manufacture certainty to make a decision sound strong. If the evidence is thin, state that the choice is a time-boxed hypothesis. A team can still move forward; it just knows what it is betting on.

Define the reversal condition before launch#

“Revisit later” is not a trigger. It is a promise that usually gets crowded out. A useful trigger is concrete enough that someone can notice it without guessing what the original author meant.

For a decision about manual review, a trigger might be: “Reopen this if the supported input types change, or if we observe repeated cases where the current fallback blocks completion.” This avoids inventing a numeric threshold when no baseline exists, while still naming the events that matter.

When a quantitative threshold is appropriate, record its denominator and source. “Review if more than five of the last fifty uploads need manual intervention” is more interpretable than “review if failure rate is high.” But only use a number the team can actually measure. A precise-looking threshold with no instrumentation is decoration.

A reversal condition should also name what is not enough. A single anecdote may prompt investigation without automatically overturning the decision. Conversely, a safety or compliance concern may require immediate review even before a recurring pattern appears. Distinguish the trigger for learning from the trigger for changing course.

Connect decisions to the work#

A log hidden in an old document will not help a team at the moment it makes a change. Link the relevant entry from the requirement, ticket, design, or launch checklist where the choice affects execution. Keep one canonical entry and reference it; copying the rationale into several places creates multiple versions that drift.

A product manager is often well placed to maintain this record, but the reasoning belongs to the people who made the choice. Ask the engineer about system constraints, the designer about interaction consequences, and the relevant domain owner about policy or operational limits. Attribute the decision to the accountable group or owner, not to a fictional consensus.

A review should be quick: scan entries whose triggers have fired, close those that no longer matter, and assign an owner to investigate the uncertain ones. If every item remains permanently “open,” the log has become a museum rather than a working tool.

Use the log to make change cheaper#

The goal is not to prevent decisions from changing. It is to make change less expensive and less personal. When someone challenges a choice, the conversation can start with the context and evidence instead of reconstructing who said what in a meeting months ago.

Before calling a PRD ready, ask:

• Which choices would surprise the team if they changed next week?
• For each one, can a new teammate find the rationale and the rejected alternative?
• Are facts and assumptions clearly distinguished?
• Is there an owner and a recognizable revisit trigger?
• Does the linked work point to one current source of truth?

If the answer is no, add only the missing decisions. A concise record of five consequential choices is more useful than a transcript of fifty conversations.