diff --git a/CHANGELOG.md b/CHANGELOG.md
index e6e8c66..ece53ad 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,9 @@
 # Changelog
 
+## 0.2.2
+
+- Add explicit markers for applied and skipped custom compaction instructions.
+
 ## 0.2.1
 
 - Add the server entrypoint expected by OpenCode's npm plugin loader.
diff --git a/README.md b/README.md
index 4581769..851244b 100644
--- a/README.md
+++ b/README.md
@@ -27,7 +27,7 @@ You can also add it manually to your global `opencode.jsonc`:
       {
         "memoryFile": ".opencode/compaction.md",
         "mode": "append",
-        "completionMarker": "Custom compaction request honored."
+        "completionMarker": "opencode-plugin-compaction-prompt: Custom compaction done."
       }
     ]
   ]
@@ -38,15 +38,17 @@ Create `.opencode/compaction.md` in the project when you have project-specific c
 
 ## Options
 
-| Option             | Default                              | Description                                                                                                |
-| ------------------ | ------------------------------------ | ---------------------------------------------------------------------------------------------------------- |
-| `memoryFile`       | `.opencode/compaction.md`            | File resolved relative to the active worktree.                                                             |
-| `mode`             | `append`                             | Append instructions to OpenCode's default prompt, or use `replace` to provide a complete prompt.           |
-| `prompt`           | "" (empty)                           | Additional instructions used together with `memoryFile`; both are included in the compaction instructions. |
-| `completionMarker` | `Custom compaction request honored.` | Exact text the model is asked to append at the end of the summary.                                         |
+| Option             | Default                                                      | Description                                                                                                |
+| ------------------ | ------------------------------------------------------------ | ---------------------------------------------------------------------------------------------------------- |
+| `memoryFile`       | `.opencode/compaction.md`                                    | File resolved relative to the active worktree.                                                             |
+| `mode`             | `append`                                                     | Append instructions to OpenCode's default prompt, or use `replace` to provide a complete prompt.           |
+| `prompt`           | "" (empty)                                                   | Additional instructions used together with `memoryFile`; both are included in the compaction instructions. |
+| `completionMarker` | `opencode-plugin-compaction-prompt: Custom compaction done.` | Exact text the model is asked to append at the end of the summary.                                         |
 
 Append mode is the recommended default because it preserves OpenCode's built-in compaction behavior. Replace mode is available when the complete prompt needs to be controlled by this plugin.
 
+When neither a prompt nor a memory file is available, the plugin adds `opencode-plugin-compaction-prompt: No custom compaction applied.` instead.
+
 ## Development
 
 ```bash
diff --git a/examples/opencode.json b/examples/opencode.json
index a66eab0..c290ea3 100644
--- a/examples/opencode.json
+++ b/examples/opencode.json
@@ -7,7 +7,7 @@
         "memoryFile": ".opencode/compaction.md",
         "mode": "append",
         "prompt": "<Example prompt for compaction>",
-        "completionMarker": "Custom compaction request honored."
+        "completionMarker": "opencode-plugin-compaction-prompt: Custom compaction done."
       }
     ]
   ]
diff --git a/src/index.ts b/src/index.ts
index 8b21b39..ab7a15c 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -13,7 +13,10 @@ export type CompactionOptions = PluginOptions & {
 
 const defaultMemoryFile = ".opencode/compaction.md";
 const defaultPrompt = "";
-const defaultCompletionMarker = "Custom compaction request honored.";
+const defaultCompletionMarker =
+  "opencode-plugin-compaction-prompt: Custom compaction done.";
+const skippedCompactionMarker =
+  "opencode-plugin-compaction-prompt: No custom compaction applied.";
 
 function asString(value: unknown): string | undefined {
   if (typeof value !== "string") {
@@ -115,6 +118,12 @@ export const CompactionPromptPlugin: Plugin = async (
       const instructions = buildInstructions(prompt, completionMarker, memory);
 
       if (!instructions) {
+        if (mode === "replace") {
+          output.prompt = skippedCompactionMarker;
+        } else {
+          output.context.push(skippedCompactionMarker);
+        }
+
         return;
       }
 
diff --git a/test/index.test.ts b/test/index.test.ts
index 0054f2d..bb81d8e 100644
--- a/test/index.test.ts
+++ b/test/index.test.ts
@@ -55,7 +55,9 @@ describe("CompactionPromptPlugin", () => {
     );
 
     expect(output.context[0]).toContain("Keep the active hypothesis.");
-    expect(output.context[0]).toContain("Custom compaction request honored.");
+    expect(output.context[0]).toContain(
+      "opencode-plugin-compaction-prompt: Custom compaction done.",
+    );
   });
 
   test("combines custom instructions with a configured memory file", async () => {
@@ -114,10 +116,12 @@ describe("CompactionPromptPlugin", () => {
     );
 
     expect(context.logs).toHaveLength(0);
-    expect(output.context).toHaveLength(0);
+    expect(output.context).toEqual([
+      "opencode-plugin-compaction-prompt: No custom compaction applied.",
+    ]);
   });
 
-  test("does not modify compaction when no instructions are provided", async () => {
+  test("adds a skipped marker when no instructions are provided", async () => {
     const context = await createContext();
     const hooks = await CompactionPromptPlugin(context as never);
     const output: { context: string[]; prompt?: string } = {
@@ -129,7 +133,10 @@ describe("CompactionPromptPlugin", () => {
       output,
     );
 
-    expect(output.context).toEqual(["Existing context"]);
+    expect(output.context).toEqual([
+      "Existing context",
+      "opencode-plugin-compaction-prompt: No custom compaction applied.",
+    ]);
     expect(output.prompt).toBeUndefined();
   });
 
@@ -147,6 +154,8 @@ describe("CompactionPromptPlugin", () => {
     );
 
     expect(context.logs).toHaveLength(1);
-    expect(output.context).toHaveLength(0);
+    expect(output.context).toEqual([
+      "opencode-plugin-compaction-prompt: No custom compaction applied.",
+    ]);
   });
 });