diff --git a/README.md b/README.md
index d9c3982..1367d41 100644
--- a/README.md
+++ b/README.md
@@ -81,8 +81,14 @@ The current project is saved automatically in browser local storage. The
   server, similar to
   [webtigerpython.ethz.ch](https://webtigerpython.ethz.ch/)
 
-ZIP projects preserve relative paths, the project name, and the configured
-Python entry point. This local format is also the shape planned for OneDrive
+ZIP projects preserve relative paths, the project name, the configured
+Python entry point, and which files are read-only (`readOnly` in
+`glpython.json`).
+
+A **read-only file** (`readOnly: true` on the file, e.g. in a share link from
+a course, as the LiaScript macro builds for its libraries) is shown with a
+lock: it can be read, run and imported, but not edited, renamed or deleted -
+e.g. a parser that learners use as a black box. This local format is also the shape planned for OneDrive
 folder synchronization.
 
 ## Microsoft sign-in
diff --git a/package-lock.json b/package-lock.json
index 4bc6764..1bc8cc7 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -10,7 +10,7 @@
       "license": "MIT",
       "dependencies": {
         "@azure/msal-browser": "^5.22.0",
-        "glpython-editor": "git+https://github.com/glpython-edu/glpython-editor.git#v0.1.18",
+        "glpython-editor": "git+https://github.com/glpython-edu/glpython-editor.git#v0.1.19",
         "jszip": "^3.10.2",
         "lucide-react": "^1.47.0",
         "lz-string": "^1.5.0",
@@ -804,7 +804,7 @@
     },
     "node_modules/glpython-editor": {
       "version": "0.1.0",
-      "resolved": "git+ssh://git@github.com/glpython-edu/glpython-editor.git#07f11de780ceec5f180bb82ddd9061f86ffad13a",
+      "resolved": "git+ssh://git@github.com/glpython-edu/glpython-editor.git#5bd8a4fe8c333a907da6ae4675bc65ff318c61a4",
       "license": "MIT",
       "peerDependencies": {
         "@monaco-editor/react": "^4.7.0",
diff --git a/package.json b/package.json
index b68930c..e81b576 100644
--- a/package.json
+++ b/package.json
@@ -12,7 +12,7 @@
   },
   "dependencies": {
     "@azure/msal-browser": "^5.22.0",
-    "glpython-editor": "git+https://github.com/glpython-edu/glpython-editor.git#v0.1.18",
+    "glpython-editor": "git+https://github.com/glpython-edu/glpython-editor.git#v0.1.19",
     "jszip": "^3.10.2",
     "lucide-react": "^1.47.0",
     "lz-string": "^1.5.0",
diff --git a/src/App.tsx b/src/App.tsx
index fb3d4f2..2a34104 100644
--- a/src/App.tsx
+++ b/src/App.tsx
@@ -1,5 +1,5 @@
 import { useEffect, useRef, useState, type KeyboardEvent as ReactKeyboardEvent } from 'react'
-import { BookOpen, CircleHelp, Download, EllipsisVertical, FileCode2, Folder, FolderOpen, Link2, Pencil, Plus, RotateCcw, Sparkles, Trash2, Upload, X } from 'lucide-react'
+import { BookOpen, CircleHelp, Download, EllipsisVertical, FileCode2, Folder, FolderOpen, Link2, Lock, Pencil, Plus, RotateCcw, Sparkles, Trash2, Upload, X } from 'lucide-react'
 import { GlPythonWorkspace, addProjectFile, deleteProjectFile, initialProject, renameProjectFile, updateProjectFile } from 'glpython-editor'
 import type { ProjectFileKind, WorkspaceCommand } from 'glpython-editor'
 import 'glpython-editor/style.css'
@@ -241,8 +241,11 @@ function App() {
           <ul className="ide-file-list">
             {filePaths.map((path) => { const file = project.files[path]; return <li key={path} className={path === activeFile ? 'active' : undefined}>
               <button type="button" className="ide-file-open" aria-current={path === activeFile ? 'true' : undefined} onClick={() => setActiveFile(path)}>{file.kind === 'python' ? <FileCode2 size={15} /> : <BookOpen size={15} />}<span>{path}</span></button>
+              {/* A read-only file (e.g. a course's library) can't be renamed or deleted either. */}
+              {file.readOnly ? <span className="ide-file-read-only" role="img" aria-label={t.readOnlyFile} title={t.readOnlyFile}><Lock size={14} /></span> : <>
               <button type="button" className="icon-button small" aria-label={t.renameFile(path)} title={t.renameFile(path)} onClick={() => renameFile(path)}><Pencil size={14} /></button>
               <button type="button" className="icon-button small ide-file-delete" aria-label={t.deleteFile(path)} title={t.deleteFile(path)} disabled={filePaths.length === 1} onClick={() => deleteFile(path)}><Trash2 size={14} /></button>
+              </>}
             </li> })}
           </ul>
           <button type="button" className="secondary-button ide-new-file" onClick={addFile}><Plus size={15} /> {t.addFile}</button>
diff --git a/src/index.css b/src/index.css
index 1df228c..7c1bec8 100644
--- a/src/index.css
+++ b/src/index.css
@@ -39,6 +39,8 @@ button { font: inherit; }
 .ide-file-open { min-width: 0; flex: 1; display: flex; align-items: center; gap: 8px; padding: 7px 8px; border: 0; color: var(--glp-text); background: none; text-align: left; font: 14px var(--glp-font-code); cursor: pointer; }
 .ide-file-open span { overflow: hidden; text-overflow: ellipsis; white-space: nowrap; }
 .ide-file-delete:not(:disabled):hover { color: var(--glp-error); }
+/* In place of rename/delete for a read-only file (e.g. a course's library). */
+.ide-file-read-only { display: inline-grid; place-items: center; padding: 6px; color: var(--glp-text-muted); }
 .ide-new-file { align-self: flex-start; }
 .ide-main { min-width: 0; min-height: 0; flex: 1; display: flex; flex-direction: column; gap: 10px; padding: 14px 16px 16px; }
 
diff --git a/src/projectShare.ts b/src/projectShare.ts
index 115466e..05a23aa 100644
--- a/src/projectShare.ts
+++ b/src/projectShare.ts
@@ -2,7 +2,8 @@ import { compressToEncodedURIComponent, decompressFromEncodedURIComponent } from
 import type { Project, ProjectFile } from 'glpython-editor'
 
 // URL query parameter used to carry a whole project (name, main file, and
-// every file's path/label/kind/code), the same idea as webTigerPython's
+// every file's path/label/kind/code, and readOnly for a file to read only,
+// e.g. a course's library), the same idea as webTigerPython's
 // `?code=` parameter but extended to a full multi-file project instead of a
 // single source string.
 const SHARE_PARAM = 'project'
@@ -26,6 +27,7 @@ function isProjectFile(value: unknown): value is ProjectFile {
   if (!value || typeof value !== 'object') return false
   const file = value as Partial<ProjectFile>
   return typeof file.path === 'string' && typeof file.label === 'string' && typeof file.code === 'string' && (file.kind === 'python' || file.kind === 'text')
+    && (file.readOnly === undefined || typeof file.readOnly === 'boolean')
 }
 
 function isSharedProjectPayload(value: unknown): value is SharedProjectPayload {
diff --git a/src/projectStorage.ts b/src/projectStorage.ts
index 049d291..df3a6eb 100644
--- a/src/projectStorage.ts
+++ b/src/projectStorage.ts
@@ -7,6 +7,14 @@ type DirectoryPickerWindow = Window & {
   showDirectoryPicker?: () => Promise<FileSystemDirectoryHandle>
 }
 
+type ProjectMetadata = { name?: string; mainFile?: string; readOnly?: string[] }
+
+// The files glpython.json lists as read-only, marked so.
+function withReadOnly(files: Record<string, ProjectFile>, metadata: ProjectMetadata): Record<string, ProjectFile> {
+  const readOnly = Array.isArray(metadata.readOnly) ? metadata.readOnly : []
+  return Object.fromEntries(Object.entries(files).map(([path, file]) => [path, readOnly.includes(path) ? { ...file, readOnly: true } : file]))
+}
+
 export function loadLocalProject(fallback: Project): Project {
   const savedProject = localStorage.getItem(storageKey)
   if (!savedProject) return fallback
@@ -29,7 +37,10 @@ export function clearLocalProject(): void {
 export async function exportProjectZip(project: Project): Promise<Blob> {
   const zip = new JSZip()
   for (const file of Object.values(project.files)) zip.file(file.path, file.code)
-  zip.file('glpython.json', JSON.stringify({ name: project.name, mainFile: project.mainFile }, null, 2))
+  // Which files are read-only (e.g. a course's library) travels in the
+  // metadata, so a ZIP round trip keeps it.
+  const readOnly = Object.values(project.files).filter((file) => file.readOnly).map((file) => file.path)
+  zip.file('glpython.json', JSON.stringify({ name: project.name, mainFile: project.mainFile, ...(readOnly.length > 0 ? { readOnly } : {}) }, null, 2))
   return zip.generateAsync({ type: 'blob' })
 }
 
@@ -37,13 +48,13 @@ export async function importProjectZip(file: File, fallback: Project): Promise<P
   const zip = await JSZip.loadAsync(file)
   const entries = Object.values(zip.files).filter((entry) => !entry.dir && entry.name !== 'glpython.json' && !entry.name.startsWith('__MACOSX/'))
   const metadataEntry = zip.file('glpython.json')
-  const metadata = metadataEntry ? JSON.parse(await metadataEntry.async('text')) as { name?: string; mainFile?: string } : {}
+  const metadata = metadataEntry ? JSON.parse(await metadataEntry.async('text')) as ProjectMetadata : {}
   const files = await Promise.all(entries.map(async (entry) => {
     const path = entry.name.replace(/^\/+/, '')
     const code = await entry.async('text')
     return [path, createProjectFile(path, code)] as const
   }))
-  const importedFiles = Object.fromEntries(files)
+  const importedFiles = withReadOnly(Object.fromEntries(files), metadata)
   const pythonFiles = Object.values(importedFiles).filter((entry) => entry.kind === 'python')
   const mainFile = metadata.mainFile && importedFiles[metadata.mainFile]
     ? metadata.mainFile
@@ -59,9 +70,9 @@ export async function importProjectFolder(fallback: Project): Promise<Project |
   const directory = await pickerWindow.showDirectoryPicker()
   const files: ProjectFile[] = []
   await readDirectory(directory, '', files)
-  const importedFiles = Object.fromEntries(files.map((file) => [file.path, file]))
-  const pythonFiles = files.filter((file) => file.kind === 'python')
   const metadata = await readProjectMetadata(directory)
+  const importedFiles = withReadOnly(Object.fromEntries(files.map((file) => [file.path, file])), metadata)
+  const pythonFiles = files.filter((file) => file.kind === 'python')
   const mainFile = metadata.mainFile && importedFiles[metadata.mainFile]
     ? metadata.mainFile
     : importedFiles['main.py']
@@ -70,11 +81,11 @@ export async function importProjectFolder(fallback: Project): Promise<Project |
   return { ...fallback, name: metadata.name || directory.name, mainFile, files: importedFiles }
 }
 
-async function readProjectMetadata(directory: FileSystemDirectoryHandle): Promise<{ name?: string; mainFile?: string }> {
+async function readProjectMetadata(directory: FileSystemDirectoryHandle): Promise<ProjectMetadata> {
   try {
     const metadataHandle = await directory.getFileHandle('glpython.json')
     const metadataFile = await metadataHandle.getFile()
-    return JSON.parse(await metadataFile.text()) as { name?: string; mainFile?: string }
+    return JSON.parse(await metadataFile.text()) as ProjectMetadata
   } catch {
     return {}
   }