diff --git a/src/serve_style.js b/src/serve_style.js
index 7de4f06..3c0c75a 100644
--- a/src/serve_style.js
+++ b/src/serve_style.js
@@ -7,44 +7,12 @@ import clone from 'clone';
 import express from 'express';
 import { validateStyleMin } from '@maplibre/maplibre-gl-style-spec';
 
-import { getPublicUrl } from './utils.js';
+import { fixUrl, allowedOptions } from './utils.js';
 
 const httpTester = /^https?:\/\//i;
-const allowedSpriteScales = allowedOptions(['', '@2x', '@3x'], '');
+const allowedSpriteScales = allowedOptions(['', '@2x', '@3x']);
 const allowedSpriteFormats = allowedOptions(['png', 'json']);
 
-/**
- *
- * @param opts
- * @param root0
- * @param root0.defaultValue
- */
-function allowedOptions(opts, { defaultValue } = {}) {
-  const values = Object.fromEntries(opts.map((key) => [key, key]));
-  return (value) => values[value] || defaultValue;
-}
-
-/**
- *
- * @param req
- * @param url
- * @param publicUrl
- */
-function fixUrl(req, url, publicUrl) {
-  if (!url || typeof url !== 'string' || url.indexOf('local://') !== 0) {
-    return url;
-  }
-  const queryParams = [];
-  if (req.query.key) {
-    queryParams.unshift(`key=${encodeURIComponent(req.query.key)}`);
-  }
-  let query = '';
-  if (queryParams.length) {
-    query = `?${queryParams.join('&')}`;
-  }
-  return url.replace('local://', getPublicUrl(publicUrl, req)) + query;
-}
-
 export const serve_style = {
   init: (options, repo) => {
     const app = express().disable('x-powered-by');
diff --git a/src/utils.js b/src/utils.js
index 2a516bc..b5b737b 100644
--- a/src/utils.js
+++ b/src/utils.js
@@ -6,6 +6,38 @@ import fs, { existsSync } from 'node:fs';
 import clone from 'clone';
 import glyphCompose from '@mapbox/glyph-pbf-composite';
 
+/**
+ * Restrict user input to an allowed set of options.
+ * @param opts
+ * @param root0
+ * @param root0.defaultValue
+ */
+export function allowedOptions(opts, { defaultValue } = {}) {
+  const values = Object.fromEntries(opts.map((key) => [key, key]));
+  return (value) => values[value] || defaultValue;
+}
+
+/**
+ * Replace local:// urls with public http(s):// urls
+ * @param req
+ * @param url
+ * @param publicUrl
+ */
+export function fixUrl(req, url, publicUrl) {
+  if (!url || typeof url !== 'string' || url.indexOf('local://') !== 0) {
+    return url;
+  }
+  const queryParams = [];
+  if (req.query.key) {
+    queryParams.unshift(`key=${encodeURIComponent(req.query.key)}`);
+  }
+  let query = '';
+  if (queryParams.length) {
+    query = `?${queryParams.join('&')}`;
+  }
+  return url.replace('local://', getPublicUrl(publicUrl, req)) + query;
+}
+
 /**
  * Generate new URL object
  * @param req