diff --git a/tools/asciicast_ezgif_durations.fish b/tools/asciicast_ezgif_durations.fish
new file mode 100644
index 00000000..2726d039
--- /dev/null
+++ b/tools/asciicast_ezgif_durations.fish
@@ -0,0 +1,17 @@
+function asciicast_ezgif_durations -a file
+    set -l times (string match -rg "^\[([\d.]*)" <$file)
+
+    set -l durations # Durations in hundredths of seconds
+
+    set -l prev_time $times[1]
+    for time in $times[2..]
+        set -a durations (math --scale=0 "($time - $prev_time) * 100")
+        set prev_time $time
+    end
+
+    set -l file_text (cat $file)
+    for duration in $durations
+        string replace -r "^\[[\d.]*" $duration $file_text[1]
+        set -e file_text[1]
+    end >$file
+end