diff --git a/packages/cli-json-cas/src/cli.test.ts b/packages/cli-json-cas/src/cli.test.ts
index 90146d5..a024a2a 100644
--- a/packages/cli-json-cas/src/cli.test.ts
+++ b/packages/cli-json-cas/src/cli.test.ts
@@ -315,6 +315,594 @@ describe("ucas render command", () => {
   });
 });
 
+// ---- Issue #50: Schema Validation in put Command ----
+
+describe("Issue #50: Schema Validation in put", () => {
+  describe("Test Group 1: Valid Data (Regression Tests)", () => {
+    test("T1.1: Valid data matching schema should be accepted", async () => {
+      const tmpStore = mkdtempSync(join(tmpdir(), "json-cas-test-"));
+      try {
+        await runCli(["init"], tmpStore);
+
+        // Create schema with required name property
+        const schemaFile = join(tmpStore, "schema.json");
+        writeFileSync(
+          schemaFile,
+          JSON.stringify({
+            type: "object",
+            properties: { name: { type: "string" } },
+            required: ["name"],
+            additionalProperties: false,
+          }),
+        );
+        const { stdout: schemaHash } = await runCli(
+          ["schema", "put", schemaFile],
+          tmpStore,
+        );
+
+        // Create valid payload
+        const payloadFile = join(tmpStore, "payload.json");
+        writeFileSync(payloadFile, JSON.stringify({ name: "test" }));
+
+        const { stdout, stderr, exitCode } = await runCli(
+          ["put", schemaHash.trim(), payloadFile],
+          tmpStore,
+        );
+
+        expect(exitCode).toBe(0);
+        expect(stderr).toBe("");
+        expect(stdout.trim()).toMatch(/^[0-9A-HJKMNP-TV-Z]{13}$/);
+
+        // Verify node was stored
+        const hash = stdout.trim();
+        const { exitCode: hasExitCode } = await runCli(["has", hash], tmpStore);
+        expect(hasExitCode).toBe(0);
+      } finally {
+        rmSync(tmpStore, { recursive: true, force: true });
+      }
+    });
+
+    test("T1.2: Valid data with optional properties should be accepted", async () => {
+      const tmpStore = mkdtempSync(join(tmpdir(), "json-cas-test-"));
+      try {
+        await runCli(["init"], tmpStore);
+
+        // Schema with optional property
+        const schemaFile = join(tmpStore, "schema.json");
+        writeFileSync(
+          schemaFile,
+          JSON.stringify({
+            type: "object",
+            properties: {
+              name: { type: "string" },
+              age: { type: "number" },
+            },
+            required: ["name"],
+            additionalProperties: false,
+          }),
+        );
+        const { stdout: schemaHash } = await runCli(
+          ["schema", "put", schemaFile],
+          tmpStore,
+        );
+
+        // Payload with only required properties
+        const payloadFile = join(tmpStore, "payload.json");
+        writeFileSync(payloadFile, JSON.stringify({ name: "test" }));
+
+        const { exitCode, stdout } = await runCli(
+          ["put", schemaHash.trim(), payloadFile],
+          tmpStore,
+        );
+
+        expect(exitCode).toBe(0);
+        expect(stdout.trim()).toMatch(/^[0-9A-HJKMNP-TV-Z]{13}$/);
+      } finally {
+        rmSync(tmpStore, { recursive: true, force: true });
+      }
+    });
+
+    test("T1.3: Valid data with nested objects should be accepted", async () => {
+      const tmpStore = mkdtempSync(join(tmpdir(), "json-cas-test-"));
+      try {
+        await runCli(["init"], tmpStore);
+
+        // Schema with nested structure
+        const schemaFile = join(tmpStore, "schema.json");
+        writeFileSync(
+          schemaFile,
+          JSON.stringify({
+            type: "object",
+            properties: {
+              name: { type: "string" },
+              address: {
+                type: "object",
+                properties: {
+                  street: { type: "string" },
+                  city: { type: "string" },
+                },
+              },
+            },
+            additionalProperties: false,
+          }),
+        );
+        const { stdout: schemaHash } = await runCli(
+          ["schema", "put", schemaFile],
+          tmpStore,
+        );
+
+        // Payload with nested structure
+        const payloadFile = join(tmpStore, "payload.json");
+        writeFileSync(
+          payloadFile,
+          JSON.stringify({
+            name: "test",
+            address: { street: "123 Main", city: "NYC" },
+          }),
+        );
+
+        const { exitCode, stdout } = await runCli(
+          ["put", schemaHash.trim(), payloadFile],
+          tmpStore,
+        );
+
+        expect(exitCode).toBe(0);
+        expect(stdout.trim()).toMatch(/^[0-9A-HJKMNP-TV-Z]{13}$/);
+      } finally {
+        rmSync(tmpStore, { recursive: true, force: true });
+      }
+    });
+
+    test("T1.4: Valid data using @ alias for type-hash should be accepted", async () => {
+      const tmpStore = mkdtempSync(join(tmpdir(), "json-cas-test-"));
+      try {
+        await runCli(["init"], tmpStore);
+
+        const payloadFile = join(tmpStore, "payload.json");
+        writeFileSync(payloadFile, JSON.stringify("hello world"));
+
+        const { exitCode, stdout } = await runCli(
+          ["put", "@string", payloadFile],
+          tmpStore,
+        );
+
+        expect(exitCode).toBe(0);
+        expect(stdout.trim()).toMatch(/^[0-9A-HJKMNP-TV-Z]{13}$/);
+      } finally {
+        rmSync(tmpStore, { recursive: true, force: true });
+      }
+    });
+  });
+
+  describe("Test Group 2: Type Mismatches (New Validation)", () => {
+    test("T2.1: Wrong property type should be rejected", async () => {
+      const tmpStore = mkdtempSync(join(tmpdir(), "json-cas-test-"));
+      try {
+        await runCli(["init"], tmpStore);
+
+        // Schema with name as string
+        const schemaFile = join(tmpStore, "schema.json");
+        writeFileSync(
+          schemaFile,
+          JSON.stringify({
+            type: "object",
+            properties: { name: { type: "string" } },
+            required: ["name"],
+            additionalProperties: false,
+          }),
+        );
+        const { stdout: schemaHash } = await runCli(
+          ["schema", "put", schemaFile],
+          tmpStore,
+        );
+
+        // Payload with name as number
+        const payloadFile = join(tmpStore, "payload.json");
+        writeFileSync(payloadFile, JSON.stringify({ name: 123 }));
+
+        const { exitCode, stdout, stderr } = await runCli(
+          ["put", schemaHash.trim(), payloadFile],
+          tmpStore,
+        );
+
+        expect(exitCode).toBe(1);
+        expect(stdout).toBe("");
+        expect(stderr).toContain("Validation failed");
+        expect(stderr).toContain(schemaHash.trim());
+        expect(stderr).toContain(payloadFile);
+
+        // Verify no node was stored
+        const { stdout: hasOutput } = await runCli(
+          ["has", "0000000000000"],
+          tmpStore,
+        );
+        expect(hasOutput.trim()).toBe("false");
+      } finally {
+        rmSync(tmpStore, { recursive: true, force: true });
+      }
+    });
+
+    test("T2.2: Missing required property should be rejected", async () => {
+      const tmpStore = mkdtempSync(join(tmpdir(), "json-cas-test-"));
+      try {
+        await runCli(["init"], tmpStore);
+
+        // Schema with required name
+        const schemaFile = join(tmpStore, "schema.json");
+        writeFileSync(
+          schemaFile,
+          JSON.stringify({
+            type: "object",
+            properties: { name: { type: "string" } },
+            required: ["name"],
+            additionalProperties: false,
+          }),
+        );
+        const { stdout: schemaHash } = await runCli(
+          ["schema", "put", schemaFile],
+          tmpStore,
+        );
+
+        // Empty payload
+        const payloadFile = join(tmpStore, "payload.json");
+        writeFileSync(payloadFile, JSON.stringify({}));
+
+        const { exitCode, stderr } = await runCli(
+          ["put", schemaHash.trim(), payloadFile],
+          tmpStore,
+        );
+
+        expect(exitCode).not.toBe(0);
+        expect(stderr).toContain("Validation failed");
+      } finally {
+        rmSync(tmpStore, { recursive: true, force: true });
+      }
+    });
+
+    test("T2.3: Additional properties when disallowed should be rejected", async () => {
+      const tmpStore = mkdtempSync(join(tmpdir(), "json-cas-test-"));
+      try {
+        await runCli(["init"], tmpStore);
+
+        // Schema with additionalProperties: false
+        const schemaFile = join(tmpStore, "schema.json");
+        writeFileSync(
+          schemaFile,
+          JSON.stringify({
+            type: "object",
+            properties: { name: { type: "string" } },
+            additionalProperties: false,
+          }),
+        );
+        const { stdout: schemaHash } = await runCli(
+          ["schema", "put", schemaFile],
+          tmpStore,
+        );
+
+        // Payload with extra property
+        const payloadFile = join(tmpStore, "payload.json");
+        writeFileSync(
+          payloadFile,
+          JSON.stringify({ name: "test", extra: "not allowed" }),
+        );
+
+        const { exitCode, stderr } = await runCli(
+          ["put", schemaHash.trim(), payloadFile],
+          tmpStore,
+        );
+
+        expect(exitCode).not.toBe(0);
+        expect(stderr).toContain("Validation failed");
+      } finally {
+        rmSync(tmpStore, { recursive: true, force: true });
+      }
+    });
+
+    test("T2.4: Wrong root type should be rejected", async () => {
+      const tmpStore = mkdtempSync(join(tmpdir(), "json-cas-test-"));
+      try {
+        await runCli(["init"], tmpStore);
+
+        // Schema expecting array
+        const schemaFile = join(tmpStore, "schema.json");
+        writeFileSync(
+          schemaFile,
+          JSON.stringify({
+            type: "array",
+            items: { type: "string" },
+          }),
+        );
+        const { stdout: schemaHash } = await runCli(
+          ["schema", "put", schemaFile],
+          tmpStore,
+        );
+
+        // Payload is an object
+        const payloadFile = join(tmpStore, "payload.json");
+        writeFileSync(payloadFile, JSON.stringify({}));
+
+        const { exitCode, stderr } = await runCli(
+          ["put", schemaHash.trim(), payloadFile],
+          tmpStore,
+        );
+
+        expect(exitCode).not.toBe(0);
+        expect(stderr).toContain("Validation failed");
+      } finally {
+        rmSync(tmpStore, { recursive: true, force: true });
+      }
+    });
+
+    test("T2.5: Nested type mismatch should be rejected", async () => {
+      const tmpStore = mkdtempSync(join(tmpdir(), "json-cas-test-"));
+      try {
+        await runCli(["init"], tmpStore);
+
+        // Schema with nested object
+        const schemaFile = join(tmpStore, "schema.json");
+        writeFileSync(
+          schemaFile,
+          JSON.stringify({
+            type: "object",
+            properties: {
+              user: {
+                type: "object",
+                properties: {
+                  age: { type: "number" },
+                },
+              },
+            },
+          }),
+        );
+        const { stdout: schemaHash } = await runCli(
+          ["schema", "put", schemaFile],
+          tmpStore,
+        );
+
+        // Payload with wrong nested type
+        const payloadFile = join(tmpStore, "payload.json");
+        writeFileSync(
+          payloadFile,
+          JSON.stringify({ user: { age: "not a number" } }),
+        );
+
+        const { exitCode, stderr } = await runCli(
+          ["put", schemaHash.trim(), payloadFile],
+          tmpStore,
+        );
+
+        expect(exitCode).not.toBe(0);
+        expect(stderr).toContain("Validation failed");
+      } finally {
+        rmSync(tmpStore, { recursive: true, force: true });
+      }
+    });
+  });
+
+  describe("Test Group 3: Schema Errors (Edge Cases)", () => {
+    test("T3.1: Non-existent type-hash should fail gracefully", async () => {
+      const tmpStore = mkdtempSync(join(tmpdir(), "json-cas-test-"));
+      try {
+        await runCli(["init"], tmpStore);
+
+        const payloadFile = join(tmpStore, "payload.json");
+        writeFileSync(payloadFile, JSON.stringify({ name: "test" }));
+
+        const { exitCode, stderr } = await runCli(
+          ["put", "ZZZZZZZZZZZZZ", payloadFile],
+          tmpStore,
+        );
+
+        expect(exitCode).not.toBe(0);
+        expect(stderr).toContain("Schema not found");
+      } finally {
+        rmSync(tmpStore, { recursive: true, force: true });
+      }
+    });
+
+    test("T3.3: Invalid @ alias should fail before validation", async () => {
+      const tmpStore = mkdtempSync(join(tmpdir(), "json-cas-test-"));
+      try {
+        await runCli(["init"], tmpStore);
+
+        const payloadFile = join(tmpStore, "payload.json");
+        writeFileSync(payloadFile, JSON.stringify({}));
+
+        const { exitCode, stderr } = await runCli(
+          ["put", "@nonexistent", payloadFile],
+          tmpStore,
+        );
+
+        expect(exitCode).not.toBe(0);
+        expect(stderr).toContain("Schema not found");
+      } finally {
+        rmSync(tmpStore, { recursive: true, force: true });
+      }
+    });
+  });
+
+  describe("Test Group 4: Integration with Existing Features", () => {
+    test("T4.1: Hash command should not validate (dry-run consistency)", async () => {
+      const tmpStore = mkdtempSync(join(tmpdir(), "json-cas-test-"));
+      try {
+        await runCli(["init"], tmpStore);
+
+        // Create schema
+        const schemaFile = join(tmpStore, "schema.json");
+        writeFileSync(
+          schemaFile,
+          JSON.stringify({
+            type: "object",
+            properties: { name: { type: "string" } },
+            required: ["name"],
+            additionalProperties: false,
+          }),
+        );
+        const { stdout: schemaHash } = await runCli(
+          ["schema", "put", schemaFile],
+          tmpStore,
+        );
+
+        // Invalid payload
+        const payloadFile = join(tmpStore, "payload.json");
+        writeFileSync(payloadFile, JSON.stringify({ name: 123 }));
+
+        // Hash command should succeed even with invalid data
+        const { exitCode, stdout } = await runCli(
+          ["hash", schemaHash.trim(), payloadFile],
+          tmpStore,
+        );
+
+        expect(exitCode).toBe(0);
+        expect(stdout.trim()).toMatch(/^[0-9A-HJKMNP-TV-Z]{13}$/);
+      } finally {
+        rmSync(tmpStore, { recursive: true, force: true });
+      }
+    });
+
+    test("T4.2: Validation respects cas_ref format in schemas", async () => {
+      const tmpStore = mkdtempSync(join(tmpdir(), "json-cas-test-"));
+      try {
+        await runCli(["init"], tmpStore);
+
+        // Schema with cas_ref format
+        const schemaFile = join(tmpStore, "schema.json");
+        writeFileSync(
+          schemaFile,
+          JSON.stringify({
+            type: "object",
+            properties: {
+              ref: { type: "string", format: "cas_ref" },
+            },
+          }),
+        );
+        const { stdout: schemaHash } = await runCli(
+          ["schema", "put", schemaFile],
+          tmpStore,
+        );
+
+        // Valid cas_ref
+        const validFile = join(tmpStore, "valid.json");
+        writeFileSync(validFile, JSON.stringify({ ref: "0000000000000" }));
+
+        const { exitCode: validExitCode } = await runCli(
+          ["put", schemaHash.trim(), validFile],
+          tmpStore,
+        );
+        expect(validExitCode).toBe(0);
+
+        // Invalid cas_ref (wrong length)
+        const invalidFile = join(tmpStore, "invalid.json");
+        writeFileSync(invalidFile, JSON.stringify({ ref: "short" }));
+
+        const { exitCode: invalidExitCode, stderr } = await runCli(
+          ["put", schemaHash.trim(), invalidFile],
+          tmpStore,
+        );
+        expect(invalidExitCode).not.toBe(0);
+        expect(stderr).toContain("Validation failed");
+      } finally {
+        rmSync(tmpStore, { recursive: true, force: true });
+      }
+    });
+
+    test("T4.3: Schema self-validation still works", async () => {
+      const tmpStore = mkdtempSync(join(tmpdir(), "json-cas-test-"));
+      try {
+        await runCli(["init"], tmpStore);
+
+        // Valid schema
+        const schemaFile = join(tmpStore, "schema.json");
+        writeFileSync(
+          schemaFile,
+          JSON.stringify({
+            type: "object",
+            properties: { name: { type: "string" } },
+          }),
+        );
+
+        const { exitCode } = await runCli(
+          ["schema", "put", schemaFile],
+          tmpStore,
+        );
+        expect(exitCode).toBe(0);
+      } finally {
+        rmSync(tmpStore, { recursive: true, force: true });
+      }
+    });
+  });
+
+  describe("Test Group 5: Error Message Quality", () => {
+    test("T5.1: Error message should be helpful", async () => {
+      const tmpStore = mkdtempSync(join(tmpdir(), "json-cas-test-"));
+      try {
+        await runCli(["init"], tmpStore);
+
+        const schemaFile = join(tmpStore, "schema.json");
+        writeFileSync(
+          schemaFile,
+          JSON.stringify({
+            type: "object",
+            properties: { name: { type: "string" } },
+            required: ["name"],
+          }),
+        );
+        const { stdout: schemaHash } = await runCli(
+          ["schema", "put", schemaFile],
+          tmpStore,
+        );
+
+        const payloadFile = join(tmpStore, "payload.json");
+        writeFileSync(payloadFile, JSON.stringify({ name: 123 }));
+
+        const { stderr } = await runCli(
+          ["put", schemaHash.trim(), payloadFile],
+          tmpStore,
+        );
+
+        expect(stderr).toContain("Validation failed");
+        expect(stderr).toContain(schemaHash.trim());
+        expect(stderr).toContain(payloadFile);
+      } finally {
+        rmSync(tmpStore, { recursive: true, force: true });
+      }
+    });
+
+    test("T5.2: Error should go to stderr, not stdout", async () => {
+      const tmpStore = mkdtempSync(join(tmpdir(), "json-cas-test-"));
+      try {
+        await runCli(["init"], tmpStore);
+
+        const schemaFile = join(tmpStore, "schema.json");
+        writeFileSync(
+          schemaFile,
+          JSON.stringify({
+            type: "object",
+            properties: { name: { type: "string" } },
+          }),
+        );
+        const { stdout: schemaHash } = await runCli(
+          ["schema", "put", schemaFile],
+          tmpStore,
+        );
+
+        const payloadFile = join(tmpStore, "payload.json");
+        writeFileSync(payloadFile, JSON.stringify({ name: 123 }));
+
+        const { stdout, stderr } = await runCli(
+          ["put", schemaHash.trim(), payloadFile],
+          tmpStore,
+        );
+
+        expect(stdout).toBe("");
+        expect(stderr.length).toBeGreaterThan(0);
+      } finally {
+        rmSync(tmpStore, { recursive: true, force: true });
+      }
+    });
+  });
+});
+
 describe("Suite 6: CLI Integration with Templates", () => {
   test("6.1 CLI with Template (Default Parameters)", async () => {
     const tmpStore = mkdtempSync(join(tmpdir(), "json-cas-test-"));
diff --git a/packages/cli-json-cas/src/index.ts b/packages/cli-json-cas/src/index.ts
index 51bdf4d..1472d06 100644
--- a/packages/cli-json-cas/src/index.ts
+++ b/packages/cli-json-cas/src/index.ts
@@ -294,6 +294,23 @@ async function cmdPut(args: string[]): Promise<void> {
   const typeHash = await resolveTypeHash(typeHashOrAlias);
   const payload = readJsonFile(file);
   const store = openStore();
+
+  // Check if schema exists
+  const schema = getSchema(store, typeHash);
+  if (schema === null) {
+    console.error(`Schema not found: ${typeHash}`);
+    process.exit(1);
+  }
+
+  // Validate payload against schema before storing
+  const tempNode = { type: typeHash, payload, timestamp: Date.now() };
+  if (!validate(store, tempNode)) {
+    console.error(
+      `Validation failed: payload in ${file} does not match schema ${typeHash}`,
+    );
+    process.exit(1);
+  }
+
   const hash = await store.put(typeHash, payload);
   console.log(hash);
 }