diff --git a/web/workspace/src/lib/workspace/settings/DecodalSourceEditor.browser.spec.ts b/web/workspace/src/lib/workspace/settings/DecodalSourceEditor.browser.spec.ts
new file mode 100644
index 000000000..baf7c6a9f
--- /dev/null
+++ b/web/workspace/src/lib/workspace/settings/DecodalSourceEditor.browser.spec.ts
@@ -0,0 +1,153 @@
+// @vitest-environment happy-dom
+
+import {
+  type CompletionResult,
+  completionStatus,
+  startCompletion,
+} from "@codemirror/autocomplete";
+import { EditorView } from "@codemirror/view";
+import { cleanup, fireEvent, render, waitFor } from "@testing-library/svelte";
+import { afterEach, expect, test, vi } from "vitest";
+import DecodalSourceEditor from "./DecodalSourceEditor.svelte";
+
+afterEach(cleanup);
+
+function setup(
+  value: string,
+  props: {
+    readonly?: boolean;
+    fixedSchemaWrapper?: boolean;
+    onComplete?: (
+      source: string,
+      offset: number,
+      explicit: boolean,
+    ) => Promise<CompletionResult | null>;
+  } = {},
+) {
+  const onChange = vi.fn();
+  const result = render(DecodalSourceEditor, { value, onChange, ...props });
+  const content = result.container.querySelector<HTMLElement>(".cm-content")!;
+  const editor = EditorView.findFromDOM(content)!;
+  editor.focus();
+  return { ...result, content, editor, onChange };
+}
+
+test.each([
+  { name: "plain line", value: "name = 1", anchor: 8, expected: "name = 1\n" },
+  {
+    name: "object body",
+    value: "{\n  name = 1",
+    anchor: 12,
+    expected: "{\n  name = 1\n  ",
+  },
+  { name: "empty object", value: "{}", anchor: 1, expected: "{\n  \n}" },
+  {
+    name: "nested object",
+    value: "{\n  nested = {}\n}",
+    anchor: 14,
+    expected: "{\n  nested = {\n    \n  }\n}",
+  },
+])(
+  "Enter inserts an indented newline in $name",
+  async ({ value, anchor, expected }) => {
+    const { content, editor, onChange } = setup(value);
+    editor.dispatch({ selection: { anchor } });
+    expect(await fireEvent.keyDown(content, { key: "Enter", code: "Enter" }))
+      .toBe(false);
+    expect(editor.state.doc.toString()).toBe(expected);
+    expect(onChange).toHaveBeenLastCalledWith(expected);
+  },
+);
+
+test("Enter indents inside the fixed wrapper without altering its assertion", async () => {
+  const { content, editor } = setup("{} as WorkspaceConfigSchema\n", {
+    fixedSchemaWrapper: true,
+  });
+  await fireEvent.keyDown(content, { key: "Enter", code: "Enter" });
+  expect(editor.state.doc.toString()).toBe(
+    "{\n  \n} as WorkspaceConfigSchema\n",
+  );
+  expect(editor.state.selection.main.head).toBe(4);
+});
+
+test("Enter does not mutate readonly sources", async () => {
+  const value = "{\n  name = 1";
+  const { content, editor, onChange } = setup(value, { readonly: true });
+  editor.dispatch({ selection: { anchor: value.length } });
+  await fireEvent.keyDown(content, { key: "Enter", code: "Enter" });
+  expect(editor.state.doc.toString()).toBe(value);
+  expect(onChange).not.toHaveBeenCalled();
+});
+
+test("Enter adds an indented newline instead of accepting a visible completion", async () => {
+  const value = "{\n  na";
+  const { content, editor } = setup(value, {
+    onComplete: async () => ({
+      from: 4,
+      options: [{ label: "name", type: "property" }],
+    }),
+  });
+  editor.dispatch({ selection: { anchor: value.length } });
+  startCompletion(editor);
+  await waitFor(() => expect(completionStatus(editor.state)).toBe("active"));
+  // Wait past CodeMirror's completion interaction delay, so accepting a
+  // suggestion would be observable rather than ignored as an early keypress.
+  await new Promise((resolve) => setTimeout(resolve, 100));
+  await fireEvent.keyDown(content, { key: "Enter", code: "Enter" });
+  expect(editor.state.doc.toString()).toBe("{\n  na\n  ");
+  await waitFor(() => expect(completionStatus(editor.state)).toBeNull());
+});
+
+test("Tab indents the current line and Shift+Tab removes indentation", async () => {
+  const { content, editor, onChange } = setup("name = 1");
+  editor.dispatch({ selection: { anchor: 4 } });
+  expect(await fireEvent.keyDown(content, { key: "Tab", code: "Tab" })).toBe(
+    false,
+  );
+  expect(editor.state.doc.toString()).toBe("  name = 1");
+  expect(onChange).toHaveBeenLastCalledWith("  name = 1");
+  expect(editor.hasFocus).toBe(true);
+  await fireEvent.keyDown(content, { key: "Tab", code: "Tab", shiftKey: true });
+  expect(editor.state.doc.toString()).toBe("name = 1");
+  expect(onChange).toHaveBeenLastCalledWith("name = 1");
+});
+
+test("Tab and Shift+Tab indent every selected line", async () => {
+  const value = "first = 1\nsecond = 2";
+  const { content, editor } = setup(value);
+  editor.dispatch({ selection: { anchor: 0, head: value.length } });
+  await fireEvent.keyDown(content, { key: "Tab", code: "Tab" });
+  expect(editor.state.doc.toString()).toBe("  first = 1\n  second = 2");
+  await fireEvent.keyDown(content, { key: "Tab", code: "Tab", shiftKey: true });
+  expect(editor.state.doc.toString()).toBe(value);
+});
+
+test("Tab inserts indentation on a blank line", async () => {
+  const { content, editor } = setup("");
+  await fireEvent.keyDown(content, { key: "Tab", code: "Tab" });
+  expect(editor.state.doc.toString()).toBe("  ");
+});
+
+test("Tab and Shift+Tab do not mutate readonly sources", async () => {
+  const value = "  name = 1";
+  const { content, editor, onChange } = setup(value, { readonly: true });
+  await fireEvent.keyDown(content, { key: "Tab", code: "Tab" });
+  await fireEvent.keyDown(content, { key: "Tab", code: "Tab", shiftKey: true });
+  expect(editor.state.doc.toString()).toBe(value);
+  expect(onChange).not.toHaveBeenCalled();
+});
+
+test("Tab indents the schema body without modifying the fixed wrapper", async () => {
+  const value = "{\n  name = 1\n} as WorkspaceConfigSchema\n";
+  const { content, editor } = setup(value, { fixedSchemaWrapper: true });
+  editor.dispatch({ selection: { anchor: value.indexOf("name") } });
+  await fireEvent.keyDown(content, { key: "Tab", code: "Tab" });
+  expect(editor.state.doc.toString()).toBe(
+    "{\n    name = 1\n} as WorkspaceConfigSchema\n",
+  );
+  await fireEvent.keyDown(content, { key: "Tab", code: "Tab", shiftKey: true });
+  expect(editor.state.doc.toString()).toBe(value);
+  editor.dispatch({ selection: { anchor: 0 } });
+  await fireEvent.keyDown(content, { key: "Tab", code: "Tab" });
+  expect(editor.state.doc.toString()).toBe(value);
+});
diff --git a/web/workspace/src/lib/workspace/settings/DecodalSourceEditor.svelte b/web/workspace/src/lib/workspace/settings/DecodalSourceEditor.svelte
index 5fd974cec..7bb39e679 100644
--- a/web/workspace/src/lib/workspace/settings/DecodalSourceEditor.svelte
+++ b/web/workspace/src/lib/workspace/settings/DecodalSourceEditor.svelte
@@ -9,6 +9,7 @@
     type CompletionContext,
     type CompletionResult,
   } from '@codemirror/autocomplete';
+  import { indentWithTab, insertNewlineAndIndent } from '@codemirror/commands';
   import { HighlightStyle, syntaxHighlighting } from '@codemirror/language';
   import { Compartment, EditorState } from '@codemirror/state';
   import { EditorView, keymap, lineNumbers, highlightActiveLine, drawSelection, type ViewUpdate } from '@codemirror/view';
@@ -129,6 +130,8 @@
           decodal({ highlight: false }),
           syntaxHighlighting(syntaxTheme),
           autocompletion({
+            // Use the explicit keymap below so Enter never accepts a suggestion.
+            defaultKeymap: false,
             activateOnTyping: false,
             override: [
               async (context: CompletionContext) => {
@@ -139,6 +142,10 @@
             ],
           }),
           keymap.of(completionKeymapWithoutEnter),
+          keymap.of([
+            { key: 'Enter', run: insertNewlineAndIndent },
+            indentWithTab,
+          ]),
           fixedSchemaWrapperCompartment.of(
             initialFixedSchemaWrapper ? fixedSchemaWrapperExtension() : [],
           ),