diff --git a/changelog/README.md b/changelog/README.md
index 07016bcb45..0b2d3dd877 100644
--- a/changelog/README.md
+++ b/changelog/README.md
@@ -6,6 +6,39 @@ somewhat manageable:
 * Create a changelog file: `touch $(date --iso-8601=seconds | tr : _)_my_change_message`
 * We collect these files for each release and put their messages in
   `CHANGELOG.md`. The files are subsequently deleted.
-* Messages should be valid Markdown
 
-I've added an example to the commit introducing this change.
+A changelog file can contain multiple entries. Each entry starts with a tag
+word from the list below, followed by one or more lines of text in Markdown
+format. An entry should mention the GitHub PR that introduces the change or the
+GitHub issue that the change fixes.
+
+Changelog entries should be understandable as a stand-alone text; it should give
+the reader an overview of the change without needing to consult more
+documentation, but it can refer to other documentation for further information.
+A Changelog entry is allowed to be verbose, but it need not duplicate
+documentation; a link to further documentation is often enough.
+
+Example:
+
+```
+ADDED: Commodo eros. Suspendisse tincidunt mi vel metus. [#1234](https://github.com/clash-lang/clash-compiler/pull/1234)
+FIXED: Facilisis neque. Nulla mattis odio vitae tortor. [#1234](https://github.com/clash-lang/clash-compiler/issues/1234)
+```
+
+The tags we use are:
+ * ADDED:
+ * FIXED:
+ * CHANGED:
+ * DEPRECATED:
+ * REMOVED:
+ * INTERNAL NEW:
+ * INTERNAL FIX:
+ * INTERNAL CHANGE:
+ * DOCUMENTATION:
+   (meaning something that only affects documentation, not code)
+
+Usually, the name of the section in the CHANGELOG is equal to the tag;
+the exceptions are:
+ * INTERNAL NEW: Listed in a CHANGELOG section named _New internal features:_
+ * INTERNAL FIX: Listed in a CHANGELOG section named _Internal fixes:_
+ * INTERNAL CHANGE: Listed in a CHANGELOG section named _Internal changes:_