writing-postmortems

Writing postmortems

REQUIRED BACKGROUND: the technical-writing skill (hard rules, truth rules, style).

Overview

Audience: the engineer who hits something similar in a year, not the people in the room. Core principle: facts from evidence, causes from mechanisms, lessons from both, and no names. Classification: historical; once reviewed it is immutable, and corrections are dated addenda.

When to invoke, and not

Invoke after an incident is resolved, or at a stable milestone of a long one. A defect that reached users and a near miss (a guard caught what review missed) earn the same write-up. Do NOT invoke during the live incident: the runbook governs that. Not for assigning accountability: a postmortem that needs a person's name to make sense is describing a process hole. Not for a status update to stakeholders, which is a report.

Skeleton

# [System]: [the failure, as its symptom, one line]

Rules

• Blameless means structural. Name the role, the gate, the dependency, the missing guard; never the person. Blaming a person stops at "be more careful"; blaming a structure produces an action item. This governs the narrative (timeline, causes, response); action-item ownership is assignment, not blame: a role in this document, an individual in the linked tracker issue.
• The timeline is evidence, not narrative. Every entry traces to something checkable, timestamps from the systems rather than memory. Where memory is the only source, say so.
• Wrong fixes are content. The fix that made sense and did not work belongs in the document with the reasoning that made it plausible; embarrassment is not a retention policy.
• Severity comes from the org taxonomy, defined where used, not assumed. When no taxonomy exists, leave the field explicitly unassigned rather than inventing one.
• Action items follow writing-issues: outcome, owner, acceptance check, filed and linked, never left as prose intentions in the postmortem. When filing is not possible from where you sit, mark each item [to file: <who files it>]; the postmortem stays Draft until the links exist.
• Immutable once reviewed. New findings are dated addenda; a rewritten postmortem is a falsified record. The review itself goes in a sign-off line (see references/truth.md in the core skill).
• Near misses use the same skeleton, with Impact describing what would have happened, labeled as the counterfactual it is.

The decision that often follows a postmortem (a new invariant, a policy change) is recorded via recording-decisions and linked, not embedded. Runbook updates the incident exposed go through writing-runbooks in the same change as the fix; documentation is part of done, not a follow-up ticket.