diff --git a/tools/spritedata/coverage.ts b/tools/spritedata/coverage.ts
new file mode 100644
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--- /dev/null
+++ b/tools/spritedata/coverage.ts
@@ -0,0 +1,82 @@
+import {spawnSync} from 'node:child_process';
+
+// What a smogon deploy is about to delete off the server:
+//
+//   node tools/deploy/index.ts run smogon.build.ts -o /tmp/xyout
+//   node tools/spritedata/coverage.ts /tmp/xyout [smogon:/smog2/sprites]
+//
+// deploy.json5 rsyncs xy/ and xyicons/ with --delete-after, so the built tree
+// is authoritative and anything the server holds that the build doesn't make
+// is about to go. Some of that is meant to: the content-stamped leftovers from
+// when these two sets published through Manifest, and the pre-rename spellings
+// below that nothing has asked for in years. Anything else is a hole in the
+// build, and this finds it before rsync does.
+//
+// names.ts answers the same question against pokemon-showdown; this one
+// answers it against what is actually being served.
+
+let dir = process.argv[2];
+let remote = process.argv[3] ?? 'smogon:/smog2/sprites';
+if (!dir) {
+    throw new Error('usage: node tools/spritedata/coverage.ts <built dir> [remote]');
+}
+
+// A stamped name: Manifest's 8 characters of RFC4648 base32 before the
+// extension. Lowercase published names can't collide with it.
+let STAMPED = /-[A-Z2-7]{8}\.[a-z0-9]+$/;
+
+// The one-time backlog this first authoritative deploy clears. Delete these
+// once it has run; anything still matching them after that is a surprise.
+//
+// The cap spellings, hoopa-alt and darmanitan-zen-galar predate PS's renames
+// to Pikachu-Alola, Hoopa-Unbound and Darmanitan-Galar-Zen, all of which the
+// build publishes; nothing in smogon.com or forum names the old ones. The
+// strawberry sweet is spelled as the bare cream both upstream and in chatot's
+// list. The pngs are shadowed by the gifs the build ships. The subdirectories
+// are XY-era scratch that no build has ever written.
+let BACKLOG = [
+    /^(\.gitignore|manifest\.json)$/,
+    /^pikachu-(kanto|hoenn|sinnoh|unova|kalos|alola)cap\.gif$/,
+    /^(hoopa-alt|darmanitan-zen-galar)\.(gif|png)$/,
+    /^alcremie-[a-z-]+-strawberry\.gif$/,
+    /^(lokix|melmetal|meltan|pawmi|quaquaval|syclant)\.png$/,
+    /^(aback|afront|asback|asfront|back|mini|sback|sfront)\//,
+];
+
+let holes = 0;
+for (let set of ['xy', 'xyicons']) {
+    let rsync = spawnSync('rsync', [
+        '-n', '-a', '--delete-after', '--itemize-changes',
+        `${dir}/${set}/`, `${remote}/${set}`,
+    ], {encoding: 'utf8'});
+    if (rsync.status !== 0) {
+        throw new Error(`rsync ${set}: ${rsync.stderr.trim() || `exit ${rsync.status}`}`);
+    }
+
+    let stamped = 0;
+    let backlog = 0;
+    let unexplained = [];
+    for (let line of rsync.stdout.split('\n')) {
+        let m = /^\*deleting +(.*)$/.exec(line);
+        if (!m) continue;
+        let name = m[1]!;
+        if (STAMPED.test(name)) {
+            stamped++;
+        } else if (BACKLOG.some(re => re.test(name))) {
+            backlog++;
+        } else {
+            unexplained.push(name);
+        }
+    }
+
+    process.stdout.write(`${set}: ${stamped} stamped, ${backlog} backlog, ${unexplained.length} unexplained\n`);
+    for (let name of unexplained) {
+        process.stdout.write(`  ${name}\n`);
+    }
+    holes += unexplained.length;
+}
+
+if (holes) {
+    process.stderr.write(`${holes} served names the build does not make\n`);
+    process.exitCode = 1;
+}