diff --git a/openclaw.plugin.json b/openclaw.plugin.json
index a3a62702..2c858428 100644
--- a/openclaw.plugin.json
+++ b/openclaw.plugin.json
@@ -44,6 +44,10 @@
     "expansionProvider": {
       "label": "Expansion Provider",
       "help": "Provider override for lcm_expand_query sub-agent (e.g., 'anthropic')"
+    },
+    "customInstructions": {
+      "label": "Custom Instructions",
+      "help": "Natural language instructions injected into all summarization prompts (e.g., formatting rules, tone control)"
     }
   },
   "configSchema": {
@@ -111,6 +115,9 @@
       },
       "expansionProvider": {
         "type": "string"
+      },
+      "customInstructions": {
+        "type": "string"
       }
     }
   }
diff --git a/src/db/config.ts b/src/db/config.ts
index b1188c14..bf9e6bab 100644
--- a/src/db/config.ts
+++ b/src/db/config.ts
@@ -42,6 +42,8 @@ export type LcmConfig = {
   timezone: string;
   /** When true, retroactively delete HEARTBEAT_OK turn cycles from LCM storage. */
   pruneHeartbeatOk: boolean;
+  /** Custom instructions injected into all summarization prompts. */
+  customInstructions: string;
 };
 
 /** Safely coerce an unknown value to a finite number, or return undefined. */
@@ -185,5 +187,7 @@ export function resolveLcmConfig(
       env.LCM_PRUNE_HEARTBEAT_OK !== undefined
         ? env.LCM_PRUNE_HEARTBEAT_OK === "true"
         : toBool(pc.pruneHeartbeatOk) ?? false,
+    customInstructions:
+      env.LCM_CUSTOM_INSTRUCTIONS?.trim() ?? toStr(pc.customInstructions) ?? "",
   };
 }
diff --git a/src/engine.ts b/src/engine.ts
index 8ff86742..6530a09a 100644
--- a/src/engine.ts
+++ b/src/engine.ts
@@ -1234,7 +1234,7 @@ export class LcmContextEngine implements ContextEngine {
       const runtimeSummarizer = await createLcmSummarizeFromLegacyParams({
         deps: this.deps,
         legacyParams: lp,
-        customInstructions: params.customInstructions,
+        customInstructions: params.customInstructions || this.config.customInstructions || undefined,
       });
       if (runtimeSummarizer) {
         return { summarize: runtimeSummarizer.fn, summaryModel: runtimeSummarizer.model };
diff --git a/test/custom-instructions.test.ts b/test/custom-instructions.test.ts
new file mode 100644
index 00000000..a02f5b35
--- /dev/null
+++ b/test/custom-instructions.test.ts
@@ -0,0 +1,58 @@
+import { describe, it, expect } from "vitest";
+import manifest from "../openclaw.plugin.json" with { type: "json" };
+import { resolveLcmConfig } from "../src/db/config.js";
+
+describe("customInstructions config", () => {
+  it("defaults customInstructions to empty string", () => {
+    const config = resolveLcmConfig({}, {});
+    expect(config.customInstructions).toBe("");
+  });
+
+  it("reads customInstructions from plugin config", () => {
+    const config = resolveLcmConfig({}, {
+      customInstructions: "Write as a neutral documenter. Use third person.",
+    });
+    expect(config.customInstructions).toBe("Write as a neutral documenter. Use third person.");
+  });
+
+  it("env var overrides plugin config for customInstructions", () => {
+    const config = resolveLcmConfig(
+      { LCM_CUSTOM_INSTRUCTIONS: "env instructions" } as NodeJS.ProcessEnv,
+      { customInstructions: "plugin instructions" },
+    );
+    expect(config.customInstructions).toBe("env instructions");
+  });
+
+  it("trims whitespace from env var customInstructions", () => {
+    const config = resolveLcmConfig(
+      { LCM_CUSTOM_INSTRUCTIONS: "  trimmed  " } as NodeJS.ProcessEnv,
+      {},
+    );
+    expect(config.customInstructions).toBe("trimmed");
+  });
+
+  it("trims whitespace from plugin config customInstructions", () => {
+    const config = resolveLcmConfig({}, {
+      customInstructions: "  trimmed  ",
+    });
+    expect(config.customInstructions).toBe("trimmed");
+  });
+
+  it("falls through to default when plugin config value is empty string", () => {
+    const config = resolveLcmConfig({}, {
+      customInstructions: "   ",
+    });
+    expect(config.customInstructions).toBe("");
+  });
+
+  it("ignores non-string plugin config values", () => {
+    const config = resolveLcmConfig({}, {
+      customInstructions: 42,
+    });
+    expect(config.customInstructions).toBe("");
+  });
+
+  it("ships a manifest with customInstructions in schema", () => {
+    expect(manifest.configSchema.properties.customInstructions).toEqual({ type: "string" });
+  });
+});