diff --git a/.adr-dir b/.adr-dir
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--- /dev/null
+++ b/.adr-dir
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+doc/architecture/decisions
diff --git a/.gitmodules b/.gitmodules
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+++ b/.gitmodules
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+[submodule "tools/adr"]
+	path = tools/adr
+	url = git@github.com:npryce/adr-tools.git
diff --git a/doc/architecture/decisions/0001-record-architecture-decisions.md b/doc/architecture/decisions/0001-record-architecture-decisions.md
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+# 1. Record architecture decisions
+
+Date: 2024-01-05
+
+## Status
+
+Accepted
+
+## Context
+
+We need to record the architectural decisions made on this project.
+
+## Decision
+
+We will use Architecture Decision Records, as [described by Michael Nygard](http://thinkrelevance.com/blog/2011/11/15/documenting-architecture-decisions).
+
+## Consequences
+
+See Michael Nygard's article, linked above. For a lightweight ADR toolset, see Nat Pryce's [adr-tools](https://github.com/npryce/adr-tools).
diff --git a/tools/adr b/tools/adr
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+Subproject commit b3279baf9be2207d1a4f4bbd608fd0b591c72aee