diff --git a/.changeset/record-modded-from.md b/.changeset/record-modded-from.md
new file mode 100644
index 0000000..13adb87
--- /dev/null
+++ b/.changeset/record-modded-from.md
@@ -0,0 +1,5 @@
+---
+"playground-cli": minor
+---
+
+`dot mod` now records the source app's domain in `dot.json`, and `dot deploy --playground` publishes it as a `moddedFrom` field in the on-chain metadata. The playground-app can use this to display "Modded from: <domain>" attribution on app detail pages. The value is shape-validated through the same `normalizeDomain` rules as the deploying domain, so a hand-edited `dot.json` can't sneak XSS payloads into shared metadata.
diff --git a/e2e/cli/mod.test.ts b/e2e/cli/mod.test.ts
index 8a2f590..f35e24e 100644
--- a/e2e/cli/mod.test.ts
+++ b/e2e/cli/mod.test.ts
@@ -93,6 +93,7 @@ describe("dot mod — clone", () => {
 			const dotJson = JSON.parse(readFileSync(dotJsonPath, "utf-8")) as {
 				domain?: string;
 				name?: string;
+				moddedFrom?: string;
 			};
 			// `domain` is set to `targetDir` in writeDotJson() — and
 			// `targetDir` flows from defaultRepoName(), which returns a
@@ -102,6 +103,7 @@ describe("dot mod — clone", () => {
 			// documented in src/commands/mod/SetupScreen.tsx.)
 			expect(dotJson.domain).toBe(created[0]);
 			expect(dotJson.name).toBeDefined();
+			expect(dotJson.moddedFrom).toBe(TEST_DOMAIN);
 
 			// ── Step 2 side effect: ignoreModLogs() ────────────────────────
 			const gitignore = readFileSync(
diff --git a/src/commands/mod/SetupScreen.tsx b/src/commands/mod/SetupScreen.tsx
index 33158cc..6a11e64 100644
--- a/src/commands/mod/SetupScreen.tsx
+++ b/src/commands/mod/SetupScreen.tsx
@@ -111,7 +111,7 @@ export function SetupScreen({ domain, metadata: initial, registry, targetDir, on
                 await createOptionalGitBaseline(targetDir, log, sourceLogFile);
 
                 stripPostinstall(targetDir);
-                writeDotJson(targetDir, meta.name ?? domain.replace(/\.dot$/, ""), meta);
+                writeDotJson(targetDir, meta.name ?? domain.replace(/\.dot$/, ""), meta, domain);
                 ignoreModLogs(targetDir);
             },
         },
@@ -202,7 +202,7 @@ function ignoreModLogs(dir: string) {
     }
 }
 
-function writeDotJson(dir: string, name: string, meta: AppMetadata) {
+function writeDotJson(dir: string, name: string, meta: AppMetadata, sourceDomain: string) {
     const dotJsonPath = resolve(dir, "dot.json");
     let dotJson: Record<string, unknown> = {};
     if (existsSync(dotJsonPath)) {
@@ -212,6 +212,7 @@ function writeDotJson(dir: string, name: string, meta: AppMetadata) {
     }
     dotJson.domain = dir;
     dotJson.name = name;
+    dotJson.moddedFrom = sourceDomain;
     if (!dotJson.description && meta.description) dotJson.description = meta.description;
     if (!dotJson.tag && meta.tag) dotJson.tag = meta.tag;
     writeFileSync(dotJsonPath, JSON.stringify(dotJson, null, 2) + "\n");
diff --git a/src/utils/deploy/playground.test.ts b/src/utils/deploy/playground.test.ts
index 1386e04..15ba859 100644
--- a/src/utils/deploy/playground.test.ts
+++ b/src/utils/deploy/playground.test.ts
@@ -80,6 +80,7 @@ import {
     buildMetadata,
     normalizeDomain,
     readGitBranch,
+    readModdedFrom,
     readReadme,
     README_CAP_BYTES,
 } from "./playground.js";
@@ -264,18 +265,98 @@ describe("readGitBranch", () => {
     });
 });
 
+describe("readModdedFrom", () => {
+    it("returns null when dot.json is missing", () => {
+        const dir = makeTmpDir();
+        try {
+            expect(readModdedFrom(dir)).toBeNull();
+        } finally {
+            rmSync(dir, { recursive: true, force: true });
+        }
+    });
+
+    it("returns the moddedFrom value when set", () => {
+        const dir = makeTmpDir();
+        try {
+            writeFileSync(join(dir, "dot.json"), JSON.stringify({ moddedFrom: "original.dot" }));
+            expect(readModdedFrom(dir)).toBe("original.dot");
+        } finally {
+            rmSync(dir, { recursive: true, force: true });
+        }
+    });
+
+    it("returns null when the field is absent, blank, or non-string", () => {
+        const dir = makeTmpDir();
+        try {
+            writeFileSync(join(dir, "dot.json"), JSON.stringify({ name: "x" }));
+            expect(readModdedFrom(dir)).toBeNull();
+            writeFileSync(join(dir, "dot.json"), JSON.stringify({ moddedFrom: "   " }));
+            expect(readModdedFrom(dir)).toBeNull();
+            writeFileSync(join(dir, "dot.json"), JSON.stringify({ moddedFrom: 42 }));
+            expect(readModdedFrom(dir)).toBeNull();
+        } finally {
+            rmSync(dir, { recursive: true, force: true });
+        }
+    });
+
+    it("returns null when dot.json is unparseable", () => {
+        const dir = makeTmpDir();
+        try {
+            writeFileSync(join(dir, "dot.json"), "{ not json");
+            expect(readModdedFrom(dir)).toBeNull();
+        } finally {
+            rmSync(dir, { recursive: true, force: true });
+        }
+    });
+
+    it("rejects malformed domains so they can't reach published metadata", () => {
+        const dir = makeTmpDir();
+        try {
+            const cases = [
+                "<script>alert(1)</script>",
+                "<img onerror=fetch(0)>.dot",
+                "foo bar.dot",
+                "foo/bar.dot",
+                "../etc.dot",
+            ];
+            for (const moddedFrom of cases) {
+                writeFileSync(join(dir, "dot.json"), JSON.stringify({ moddedFrom }));
+                expect(readModdedFrom(dir), `expected null for ${moddedFrom}`).toBeNull();
+            }
+        } finally {
+            rmSync(dir, { recursive: true, force: true });
+        }
+    });
+
+    it("canonicalizes to <label>.dot when the suffix is missing", () => {
+        const dir = makeTmpDir();
+        try {
+            writeFileSync(join(dir, "dot.json"), JSON.stringify({ moddedFrom: "original" }));
+            expect(readModdedFrom(dir)).toBe("original.dot");
+        } finally {
+            rmSync(dir, { recursive: true, force: true });
+        }
+    });
+});
+
 describe("buildMetadata", () => {
     it("includes repository when repositoryUrl is non-null", () => {
         const meta = buildMetadata({
             repositoryUrl: "https://github.com/x/y",
             branch: null,
             readme: null,
+            moddedFrom: null,
         });
         expect(meta).toEqual({ repository: "https://github.com/x/y" });
     });
 
     it("omits repository entirely when repositoryUrl is null", () => {
-        const meta = buildMetadata({ repositoryUrl: null, branch: null, readme: null });
+        const meta = buildMetadata({
+            repositoryUrl: null,
+            branch: null,
+            readme: null,
+            moddedFrom: null,
+        });
         expect(meta.repository).toBeUndefined();
     });
 
@@ -284,12 +365,18 @@ describe("buildMetadata", () => {
             repositoryUrl: "https://github.com/x/y",
             branch: "develop",
             readme: null,
+            moddedFrom: null,
         });
         expect(meta).toEqual({ repository: "https://github.com/x/y", branch: "develop" });
     });
 
     it("omits branch when repositoryUrl is null (branch alone is meaningless)", () => {
-        const meta = buildMetadata({ repositoryUrl: null, branch: "develop", readme: null });
+        const meta = buildMetadata({
+            repositoryUrl: null,
+            branch: "develop",
+            readme: null,
+            moddedFrom: null,
+        });
         expect(meta.branch).toBeUndefined();
     });
 
@@ -298,9 +385,30 @@ describe("buildMetadata", () => {
             repositoryUrl: null,
             branch: null,
             readme: { kind: "ok", content: "hello", size: 5 },
+            moddedFrom: null,
         });
         expect(meta).toEqual({ readme: "hello" });
     });
+
+    it("includes moddedFrom when present (independent of repositoryUrl)", () => {
+        const meta = buildMetadata({
+            repositoryUrl: null,
+            branch: null,
+            readme: null,
+            moddedFrom: "original.dot",
+        });
+        expect(meta).toEqual({ moddedFrom: "original.dot" });
+    });
+
+    it("omits moddedFrom when null or empty", () => {
+        const meta = buildMetadata({
+            repositoryUrl: "https://github.com/x/y",
+            branch: null,
+            readme: null,
+            moddedFrom: null,
+        });
+        expect(meta.moddedFrom).toBeUndefined();
+    });
 });
 
 describe("publishToPlayground", () => {
diff --git a/src/utils/deploy/playground.ts b/src/utils/deploy/playground.ts
index c9b3aaa..d2eacfa 100644
--- a/src/utils/deploy/playground.ts
+++ b/src/utils/deploy/playground.ts
@@ -169,6 +169,7 @@ export function buildMetadata(input: {
     repositoryUrl: string | null;
     branch: string | null;
     readme: ReadmeStatus | null;
+    moddedFrom: string | null;
 }): Record<string, string> {
     const meta: Record<string, string> = {};
     if (input.repositoryUrl) meta.repository = input.repositoryUrl;
@@ -177,9 +178,41 @@ export function buildMetadata(input: {
     // bloat the JSON.
     if (input.repositoryUrl && input.branch) meta.branch = input.branch;
     if (input.readme && input.readme.kind === "ok") meta.readme = input.readme.content;
+    if (input.moddedFrom) meta.moddedFrom = input.moddedFrom;
     return meta;
 }
 
+/**
+ * Returns the canonical `<label>.dot` form, or `null` for any unusable value
+ * (missing file, parse fail, non-string, or a value that doesn't pass
+ * `normalizeDomain`). `dot.json` is user-editable, so we shape-validate before
+ * publishing the field on-chain — the frontend still escapes on render, but
+ * we don't propagate garbage into shared metadata.
+ */
+export function readModdedFrom(cwd: string): string | null {
+    const path = join(cwd, "dot.json");
+    let raw: string;
+    try {
+        raw = readFileSync(path, "utf8");
+    } catch {
+        return null;
+    }
+    let parsed: unknown;
+    try {
+        parsed = JSON.parse(raw);
+    } catch {
+        return null;
+    }
+    if (!parsed || typeof parsed !== "object") return null;
+    const value = (parsed as Record<string, unknown>).moddedFrom;
+    if (typeof value !== "string") return null;
+    try {
+        return normalizeDomain(value).fullDomain;
+    } catch {
+        return null;
+    }
+}
+
 export async function publishToPlayground(
     options: PublishToPlaygroundOptions,
 ): Promise<PublishToPlaygroundResult> {
@@ -192,10 +225,12 @@ export async function publishToPlayground(
     // GitHub API call per `dot mod` invocation — see
     // `src/commands/mod/SetupScreen.tsx`.
     const branch = options.cwd && options.repositoryUrl ? readGitBranch(options.cwd) : null;
+    const moddedFrom = options.cwd ? readModdedFrom(options.cwd) : null;
     const metadata = buildMetadata({
         repositoryUrl: options.repositoryUrl,
         branch,
         readme,
+        moddedFrom,
     });
 
     const metadataBytes = new Uint8Array(Buffer.from(JSON.stringify(metadata), "utf8"));