diff --git a/src/adapters/index.ts b/src/adapters/index.ts
index 974eaa14..1f765c0a 100644
--- a/src/adapters/index.ts
+++ b/src/adapters/index.ts
@@ -9,6 +9,7 @@ import { generateTypes } from "prismic-ts-codegen";
 import { glob } from "tinyglobby";
 
 import { getCredentials } from "../auth";
+import { CommandError } from "../lib/command";
 import {
 	exists,
 	readEnvFile,
@@ -28,6 +29,7 @@ import {
 import {
 	canonicalizeCustomType,
 	canonicalizeSlice,
+	getLegacySlices,
 	type Models,
 	type ModelsDiff,
 } from "../lib/prismic/models";
@@ -181,8 +183,15 @@ export abstract class Adapter {
 
 	async getSlice(id: string): Promise<ModelMeta<SharedSliceModel>> {
 		const slice = (await this.getSlices()).find((s) => s.model.id === id);
-		if (!slice) throw new Error(`No slice found with ID: ${id}`);
-		return slice;
+		if (slice) return slice;
+		const customTypes = (await this.getCustomTypes()).map((customType) => customType.model);
+		const legacySlice = getLegacySlices(customTypes).find((s) => s.id === id);
+		if (legacySlice) {
+			throw new CommandError(
+				`"${id}" is a legacy slice in "${legacySlice.customTypeId}". The CLI cannot edit legacy slices.`,
+			);
+		}
+		throw new Error(`No slice found with ID: ${id}`);
 	}
 
 	async createSlice(model: SharedSliceModel): Promise<void> {
diff --git a/src/commands/slice-list.ts b/src/commands/slice-list.ts
index 410bd030..1d2a8a14 100644
--- a/src/commands/slice-list.ts
+++ b/src/commands/slice-list.ts
@@ -1,32 +1,64 @@
 import { getAdapter } from "../adapters";
 import { createCommand, type CommandConfig } from "../lib/command";
 import { stringify } from "../lib/json";
+import { getLegacySlices } from "../lib/prismic/models";
 import { formatTable } from "../lib/string";
 
 const config = {
 	name: "prismic slice list",
-	description: "List all slices.",
+	description: `
+		List all slices.
+
+		Legacy slices from the Legacy Builder are marked with * and show the type
+		that defines them.
+	`,
 	options: {
+		legacy: { type: "boolean", description: "List only legacy slices" },
 		json: { type: "boolean", description: "Output as JSON" },
 	},
 } satisfies CommandConfig;
 
 export default createCommand(config, async ({ values }) => {
-	const { json } = values;
+	const { legacy, json } = values;
 
 	const adapter = await getAdapter();
-	const slices = await adapter.getSlices();
+	const slices = legacy ? [] : (await adapter.getSlices()).map((slice) => slice.model);
+	const customTypes = (await adapter.getCustomTypes()).map((customType) => customType.model);
+	const legacySlices = getLegacySlices(customTypes);
+
+	if (json && legacy) {
+		const rows = legacySlices.map((s) => ({
+			id: s.id,
+			definedIn: s.customTypeId,
+			sliceZone: s.sliceZoneId,
+		}));
+		console.info(stringify(rows));
+		return;
+	}
 
 	if (json) {
-		console.info(stringify(slices.map((s) => s.model)));
+		console.info(stringify(slices));
 		return;
 	}
 
-	if (slices.length === 0) {
-		console.info("No slices found.");
+	if (slices.length === 0 && legacySlices.length === 0) {
+		console.info(legacy ? "No legacy slices found." : "No slices found.");
 		return;
 	}
 
-	const rows = slices.map(({ model }) => [model.name, model.id]);
-	console.info(formatTable(rows, { headers: ["NAME", "ID"] }));
+	const rows = [
+		...slices.map((slice) => [slice.name, slice.id, ""]),
+		...legacySlices.map(({ id, model, customTypeId, sliceZoneId }) => {
+			const name = "fieldset" in model ? model.fieldset : model.config?.label;
+			return [
+				`${name || id} *`,
+				id,
+				sliceZoneId === "body" ? customTypeId : `${customTypeId} (${sliceZoneId} slice zone)`,
+			];
+		}),
+	];
+	console.info(formatTable(rows, { headers: ["NAME", "ID", "DEFINED IN"] }));
+	if (legacySlices.length > 0) {
+		console.info("\n* Legacy slice. The CLI cannot edit legacy slices.");
+	}
 });
diff --git a/src/commands/type-view.ts b/src/commands/type-view.ts
index f22df3ba..938e6ef4 100644
--- a/src/commands/type-view.ts
+++ b/src/commands/type-view.ts
@@ -2,6 +2,7 @@ import { getAdapter } from "../adapters";
 import { formatFieldTable } from "../fields";
 import { createCommand, type CommandConfig } from "../lib/command";
 import { stringify } from "../lib/json";
+import { getLegacySlices } from "../lib/prismic/models";
 import { readConfig } from "../project";
 
 const config = {
@@ -39,5 +40,16 @@ export default createCommand(config, async ({ positionals, values }) => {
 		console.info("");
 		console.info(`${tabName}:`);
 		console.info(formatFieldTable(fields));
+		for (const [fieldId, field] of Object.entries(fields)) {
+			if (field.type !== "Slices") continue;
+			const sliceIds = Object.entries(field.config?.choices ?? {}).map(([sliceId, choice]) =>
+				choice.type === "SharedSlice" ? sliceId : `${sliceId} *`,
+			);
+			console.info(`\n  ${fieldId} slices: ${sliceIds.join(", ") || "(none)"}`);
+		}
+	}
+
+	if (getLegacySlices([type]).length > 0) {
+		console.info("\n* Legacy slice. The CLI cannot edit legacy slices.");
 	}
 });
diff --git a/src/lib/prismic/models.ts b/src/lib/prismic/models.ts
index e6bc7324..e7678797 100644
--- a/src/lib/prismic/models.ts
+++ b/src/lib/prismic/models.ts
@@ -283,6 +283,31 @@ function resolveNestedFieldContainer(
 	return resolveNestedFieldContainer(remaining.join("."), field.config.fields);
 }
 
+type SliceChoice = NonNullable<NonNullable<DynamicSlicesModel["config"]>["choices"]>[string];
+
+export type LegacySlice = {
+	id: string;
+	customTypeId: string;
+	sliceZoneId: string;
+	model: Exclude<SliceChoice, { type: "SharedSlice" }>;
+};
+
+/** Slices defined inside a slice zone by the Legacy Builder. */
+export function getLegacySlices(customTypes: DynamicCustomTypeModel[]): LegacySlice[] {
+	return customTypes.flatMap((customType) =>
+		Object.values(customType.json).flatMap((tab) =>
+			Object.entries(tab).flatMap(([sliceZoneId, sliceZone]) => {
+				if (sliceZone.type !== "Slices") return [];
+				return Object.entries(sliceZone.config?.choices ?? {}).flatMap(([id, model]) =>
+					model.type === "SharedSlice"
+						? []
+						: [{ id, customTypeId: customType.id, sliceZoneId, model }],
+				);
+			}),
+		),
+	);
+}
+
 export class FieldExistsError extends Error {
 	name = "FieldExistsError";
 
diff --git a/test/it.ts b/test/it.ts
index 264dc545..bb0d1c76 100644
--- a/test/it.ts
+++ b/test/it.ts
@@ -227,6 +227,37 @@ export function buildCustomType(
 	};
 }
 
+/** A type whose "body" slice zone holds a Slice, a Group, and a field legacy slice. */
+export function buildLegacyCustomType(): DynamicCustomTypeModel {
+	return buildCustomType({
+		json: {
+			Main: {
+				body: {
+					type: "Slices",
+					config: {
+						choices: {
+							hero: {
+								type: "Slice",
+								fieldset: "Hero",
+								"non-repeat": {
+									title: { type: "StructuredText", config: { label: "Title", single: "heading1" } },
+								},
+								repeat: { label: { type: "Text", config: { label: "Label" } } },
+							},
+							gallery: {
+								type: "Group",
+								fieldset: "Gallery",
+								config: { fields: { caption: { type: "Text", config: { label: "Caption" } } } },
+							},
+							quote: { type: "Text", config: { label: "Quote" } },
+						},
+					},
+				},
+			},
+		},
+	});
+}
+
 export function buildSlice(overrides?: Partial<SharedSliceModel>): SharedSliceModel {
 	const id = crypto.randomUUID().split("-")[0];
 	return {
diff --git a/test/slice-list.test.ts b/test/slice-list.test.ts
index f8388e0d..7bbbbf58 100644
--- a/test/slice-list.test.ts
+++ b/test/slice-list.test.ts
@@ -1,4 +1,4 @@
-import { buildSlice, it, writeLocalSlice } from "./it";
+import { buildLegacyCustomType, buildSlice, it, writeLocalCustomType, writeLocalSlice } from "./it";
 
 it("supports --help", async ({ expect, prismic }) => {
 	const { stdout, stderr, exitCode } = await prismic("slice", ["list", "--help"]);
@@ -24,3 +24,25 @@ it("lists slices as JSON", async ({ expect, prismic, project }) => {
 	const parsed = JSON.parse(stdout);
 	expect(parsed).toEqual(expect.arrayContaining([expect.objectContaining({ id: slice.id })]));
 });
+
+it("marks legacy slices", async ({ expect, prismic, project }) => {
+	const customType = buildLegacyCustomType();
+	await writeLocalCustomType(project, customType);
+
+	const { stdout, stderr, exitCode } = await prismic("slice", ["list"]);
+	expect(exitCode, stderr).toBe(0);
+	expect(stdout).toMatch(new RegExp(`Hero \\*\\s+hero\\s+${customType.id}`));
+	expect(stdout).toContain("* Legacy slice. The CLI cannot edit legacy slices.");
+});
+
+it("lists only legacy slices as JSON", async ({ expect, prismic, project }) => {
+	await writeLocalSlice(project, buildSlice());
+	const customType = buildLegacyCustomType();
+	await writeLocalCustomType(project, customType);
+
+	const { stdout, stderr, exitCode } = await prismic("slice", ["list", "--legacy", "--json"]);
+	expect(exitCode, stderr).toBe(0);
+	const parsed = JSON.parse(stdout);
+	expect(parsed).toHaveLength(3);
+	expect(parsed).toContainEqual({ id: "hero", definedIn: customType.id, sliceZone: "body" });
+});
diff --git a/test/slice-view.test.ts b/test/slice-view.test.ts
index bfa6363b..ea1d8648 100644
--- a/test/slice-view.test.ts
+++ b/test/slice-view.test.ts
@@ -1,4 +1,4 @@
-import { buildSlice, it, writeLocalSlice } from "./it";
+import { buildLegacyCustomType, buildSlice, it, writeLocalCustomType, writeLocalSlice } from "./it";
 
 it("supports --help", async ({ expect, prismic }) => {
 	const { stdout, stderr, exitCode } = await prismic("slice", ["view", "--help"]);
@@ -65,3 +65,14 @@ it("views a slice as JSON", async ({ expect, prismic, project }) => {
 	const parsed = JSON.parse(stdout);
 	expect(parsed).toMatchObject({ id: slice.id, name: slice.name });
 });
+
+it("fails for a legacy slice", async ({ expect, prismic, project }) => {
+	const customType = buildLegacyCustomType();
+	await writeLocalCustomType(project, customType);
+
+	const { stderr, exitCode } = await prismic("slice", ["view", "hero"]);
+	expect(exitCode).toBe(1);
+	expect(stderr).toContain(
+		`"hero" is a legacy slice in "${customType.id}". The CLI cannot edit legacy slices.`,
+	);
+});
diff --git a/test/type-view.test.ts b/test/type-view.test.ts
index 2e4c7479..e5f98cfe 100644
--- a/test/type-view.test.ts
+++ b/test/type-view.test.ts
@@ -1,4 +1,4 @@
-import { buildCustomType, it, writeLocalCustomType } from "./it";
+import { buildCustomType, buildLegacyCustomType, it, writeLocalCustomType } from "./it";
 
 it("supports --help", async ({ expect, prismic }) => {
 	const { stdout, stderr, exitCode } = await prismic("type", ["view", "--help"]);
@@ -52,3 +52,13 @@ it("views a type as JSON", async ({ expect, prismic, project }) => {
 	const parsed = JSON.parse(stdout);
 	expect(parsed).toMatchObject({ id: customType.id, label: customType.label, format: "custom" });
 });
+
+it("marks legacy slices", async ({ expect, prismic, project }) => {
+	const customType = buildLegacyCustomType();
+	await writeLocalCustomType(project, customType);
+
+	const { stdout, stderr, exitCode } = await prismic("type", ["view", customType.id]);
+	expect(exitCode, stderr).toBe(0);
+	expect(stdout).toContain("body slices: hero *, gallery *, quote *");
+	expect(stdout).toContain("* Legacy slice.");
+});