diff --git a/src/agents/tools/pdf-tool.test.ts b/src/agents/tools/pdf-tool.test.ts
index 813cbb2e81a..0ce36b21301 100644
--- a/src/agents/tools/pdf-tool.test.ts
+++ b/src/agents/tools/pdf-tool.test.ts
@@ -287,6 +287,42 @@ describe("createPdfTool", () => {
     });
   });
 
+  it("rejects invalid maxBytesMb before loading PDFs", async () => {
+    await withConfiguredPdfTool(async (tool) => {
+      const loadSpy = vi.spyOn(webMedia, "loadWebMediaRaw");
+
+      await expect(
+        tool.execute("t1", {
+          prompt: "test",
+          pdf: "/tmp/doc.pdf",
+          maxBytesMb: 0,
+        }),
+      ).rejects.toThrow("maxBytesMb must be greater than 0");
+      expect(loadSpy).not.toHaveBeenCalled();
+    });
+  });
+
+  it("passes validated maxBytesMb to PDF loading", async () => {
+    await withTempPdfAgentDir(async (agentDir) => {
+      const { loadSpy } = await stubPdfToolInfra(agentDir, {
+        provider: "anthropic",
+        input: ["text", "document"],
+      });
+      vi.spyOn(pdfNativeProviders, "anthropicAnalyzePdf").mockResolvedValue("native summary");
+      const cfg = withPdfModel(ANTHROPIC_PDF_MODEL);
+      const tool = requirePdfTool((await loadCreatePdfTool())({ config: cfg, agentDir }));
+
+      await tool.execute("t1", {
+        prompt: "summarize",
+        pdf: "/tmp/doc.pdf",
+        maxBytesMb: "0.5",
+      });
+
+      const [, loadOptions] = firstMockCall(loadSpy, "loadWebMediaRaw");
+      expectFields(loadOptions, { maxBytes: 524_288 });
+    });
+  });
+
   it("respects fsPolicy.workspaceOnly for non-sandbox pdf paths", async () => {
     await withTempPdfAgentDir(async (agentDir) => {
       const workspaceDir = await fs.mkdtemp(path.join(os.tmpdir(), "openclaw-pdf-ws-"));
@@ -686,5 +722,9 @@ describe("createPdfTool", () => {
     expect(props).toHaveProperty("password");
     expect(props).toHaveProperty("model");
     expect(props).toHaveProperty("maxBytesMb");
+    expect(PdfToolSchema.properties.maxBytesMb).toMatchObject({
+      type: "number",
+      exclusiveMinimum: 0,
+    });
   });
 });
diff --git a/src/agents/tools/pdf-tool.ts b/src/agents/tools/pdf-tool.ts
index d379c1d585d..7b7bff1f75d 100644
--- a/src/agents/tools/pdf-tool.ts
+++ b/src/agents/tools/pdf-tool.ts
@@ -14,7 +14,8 @@ import {
 } from "../../shared/string-coerce.js";
 import { resolveUserPath } from "../../utils.js";
 import type { AuthProfileStore } from "../auth-profiles/types.js";
-import { ToolInputError } from "./common.js";
+import { optionalFiniteNumberSchema } from "../schema/typebox.js";
+import { readFiniteNumberParam, ToolInputError } from "./common.js";
 import { coerceImageModelConfig, type ImageModelConfig } from "./image-tool.helpers.js";
 import {
   applyImageModelConfigDefaults,
@@ -73,7 +74,7 @@ export const PdfToolSchema = Type.Object({
   ),
   password: Type.Optional(Type.String({ description: "Password for encrypted PDFs." })),
   model: Type.Optional(Type.String()),
-  maxBytesMb: Type.Optional(Type.Number()),
+  maxBytesMb: optionalFiniteNumberSchema({ exclusiveMinimum: 0 }),
 });
 
 // ---------------------------------------------------------------------------
@@ -354,11 +355,12 @@ export function createPdfTool(options?: {
         record,
         DEFAULT_PROMPT,
       );
-      const maxBytesMbRaw = typeof record.maxBytesMb === "number" ? record.maxBytesMb : undefined;
       const maxBytesMb =
-        typeof maxBytesMbRaw === "number" && Number.isFinite(maxBytesMbRaw) && maxBytesMbRaw > 0
-          ? maxBytesMbRaw
-          : configuredMaxBytesMb;
+        readFiniteNumberParam(record, "maxBytesMb", {
+          min: 0,
+          minExclusive: true,
+          message: "maxBytesMb must be greater than 0",
+        }) ?? configuredMaxBytesMb;
       const maxBytes = Math.floor(maxBytesMb * 1024 * 1024);
 
       // Parse page range