diff --git a/src/runtime-js.ts b/src/runtime-js.ts
index c840bb3..a67223c 100644
--- a/src/runtime-js.ts
+++ b/src/runtime-js.ts
@@ -129,20 +129,38 @@ export const _rt = {
         return { _tag: 'Some', _0: moduleDefs.map(d => prettyPrint(d)).join('\n\n') };
     },
     "saveImage!": () => {
-        const saved: Record<string, string> = {};
-        for (const [name, ast] of definitions) {
-            const source = prettyPrint({ kind: 'definition', name, body: ast });
-            saved[name] = source;
+        const modules = new Map<string, Definition[]>();
+        const standalone: Definition[] = [];
+
+        for (const [_name, def] of definitions) {
+            if (def.module) {
+                if (!modules.has(def.module)) modules.set(def.module, []);
+                modules.get(def.module)!.push(def);
+            } else {
+                standalone.push(def);
+            }
+        }
+
+        // Save modules
+        for (const [moduleName, defs] of modules) {
+            const content = '@' + moduleName + '\n\n' +
+                defs.map(d => prettyPrint(d)).join('\n\n') + '\n\n@\n';
+            fetch('/api/save', {
+                method: 'POST',
+                headers: { 'Content-Type': 'application/json' },
+                body: JSON.stringify({ filename: moduleName, content })
+            });
+        }
+
+        // Save standalone defs
+        for (const def of definitions) {
+            const content = prettyPrint(def) + '\n';
+            fetch('/api/save', {
+                method: 'POST',
+                headers: { 'Content-Type': 'application/json' },
+                body: JSON.stringify({ filename: def.name, content })
+            });
        }
-       const content = Object.values(saved).join('\n\n');
-       const blob = new Blob([content], { type: 'text/plain' });
-       const url = URL.createObjectURL(blob);
-       const a = document.createElement('a');
-       a.href = url;
-       a.download = `cg-image-${new Date().toISOString().slice(0, 19).replace(/[T:]/g, '-')}.cg`;
-       a.click();
-       URL.revokeObjectURL(url);
-       return { _tag: 'Ok' };
     },
     "saveModule!": (moduleName: string) => {
         const moduleDefs = [...definitions.values()]
@@ -160,6 +178,18 @@ export const _rt = {
 
        return { _tag: 'Defined', _0: moduleName };
     },
+    "saveDef!": (name: string) => {
+        const def = definitions.get(name);
+        if (!def) return { _tag: 'Err', _0: 'Unknown: ' + name };
+        const content = prettyPrint(def) + '\n';
+        fetch('/api/save', {
+            method: 'POST',
+            headers: { 'Content-Type': 'application/json' },
+            body: JSON.stringify({ filename: name, content })
+        });
+
+       return { _tag: 'Defined', _0: name };
+    },
     rebind: (name: string, pathOrValue: any, maybeValue?: any) => {
         if (maybeValue === undefined) {
             store[name] = pathOrValue;
@@ -240,6 +270,7 @@ export const _rt = {
                     const source = prettyPrint(def);
                     appendChangeLog(def.name, source);
                     saveDefinitions();
+                    syncToFilesystem(def.name);
                     return { _tag: 'Defined', _0: def.name };
                 }
             } catch (e: any) {
@@ -428,3 +459,27 @@ function appendChangeLog(name: string, source: string) {
         console.error('Failed to append changelog:', e);
     }
 }
+
+function syncToFilesystem(name: string) {
+    const def = definitions.get(name);
+    if (!def) return;
+
+    if (def.module) {
+        const moduleDefs = [...definitions.values()]
+            .filter(d => d.module === def.module);
+        const content = '@' + def.module + '\n\n' +
+            moduleDefs.map(d => prettyPrint(d)).join('\n\n') + '\n\n@\n';
+        fetch('/api/save', {
+            method: 'POST',
+            headers: { 'Content-Type': 'application/json' },
+            body: JSON.stringify({ filename: def.module, content })
+        });
+    } else {
+        const content = prettyPrint(def) + '\n';
+        fetch('/api/save', {
+            method: 'POST',
+            headers: { 'Content-Type': 'application/json' },
+            body: JSON.stringify({ filename: name, content })
+        });
+    }
+}