What a postmortem is
Collect the lessons of an incident systematicallyand turn them into team knowledge
The point of a postmortem is not to assign blame. It is to learn from the incident and work out what to improve. Maximising what you learn from a failure — and sharing it — is what raises reliability across the organisation.
A fixed format lowers the cost of writing one and leaves something readable behind. The example below is the minimum that works.
What goes in the report
Item
What to write
Example: demand-forecasting app, overnight job failure (SEV2)
- Summary
- What to writeWhat happened, in one sentence
- Example: demand-forecasting app, overnight job failure (SEV2)The overnight retraining job failed, so the next morning's forecast never appeared on screen
- Impact
- What to writeWhose work was affected, and how
- Example: demand-forecasting app, overnight job failure (SEV2)The business team used the previous day's forecast for morning planning. No work was halted
- Timeline
- What to writeWhen it started, was noticed and was fixed — and what was done
- Example: demand-forecasting app, overnight job failure (SEV2)02:14 job fails → 08:30 a user reports it → 09:10 cause identified → 10:05 rerun and recovered
- Cause
- What to writeWhat triggered it, and why it was not caught
- Example: demand-forecasting app, overnight job failure (SEV2)An automatic library update changed the input format and the load failed. Nothing alerted on the failure, so it went unnoticed until morning
- Preventive actions
- What to writeWhat will be done, by whom, by when
- Example: demand-forecasting app, overnight job failure (SEV2)1. Pin the version (ALBY / 30 Sep) 2. Alert automatically on failure (ALBY / 30 Sep) 3. Add a check to the update procedure (client and ALBY / 15 Oct)
Making it work in practice
When to run one
Always for SEV1 and SEV2. For SEV3 and below, run one when the same thing keeps happening, or when service came back without anyone understanding why.
Following through on the actions
A postmortem is only worth as much as the preventive actions that actually get done. Review them regularly — in the weekly team meeting and the monthly all-hands.
The culture it needs
- Psychological safety, so people can describe what really happened
- Treating postmortems as valuable work rather than paperwork
- A standing place to look back, not a one-off