diff --git a/scripts/update-docs.ts b/scripts/update-docs.ts
index 6751fc4..1cebf2a 100644
--- a/scripts/update-docs.ts
+++ b/scripts/update-docs.ts
@@ -14,6 +14,11 @@ const excludedPrefixes = [
   "apps/native/web-build/",
   "packages/backend/convex/_generated/",
 ];
+const maxPromptCharacters = 900_000;
+
+const diffExclusions = excludedPrefixes.map(
+  (prefix) => `:(exclude,glob)${prefix}**`
+);
 
 const documentationNames = new Set([
   "AGENTS.md",
@@ -229,16 +234,7 @@ try {
   const [changedFiles, documentationFiles, diffResult] = await Promise.all([
     listChangedFiles(range),
     listDocumentationFiles(),
-    run([
-      "git",
-      "diff",
-      "--binary",
-      "--find-renames",
-      range,
-      "--",
-      ".",
-      ":(exclude)repos/**",
-    ]),
+    run(["git", "diff", "--find-renames", range, "--", ".", ...diffExclusions]),
   ]);
   if (diffResult.exitCode !== 0) {
     throw new Error(
@@ -253,10 +249,16 @@ try {
     documentationFiles,
     diff: diffResult.stdout,
   });
+  if (prompt.length > maxPromptCharacters) {
+    throw new Error(
+      `Generated documentation prompt is ${prompt.length} characters, exceeding the ${maxPromptCharacters} character safety limit. Use a smaller revision range.`
+    );
+  }
 
   console.log(`Revision: ${range}`);
   console.log(`Agent: ${agent}`);
   console.log(`Changed first-party files: ${changedFiles.length}`);
+  console.log(`Prompt characters: ${prompt.length}`);
   console.log(`Command: ${formatCommand(command)} < generated-prompt`);
 
   if (values["dry-run"]) {