diff --git a/lib/entry-points.js b/lib/entry-points.js
index e9d524358..628f26fe5 100644
--- a/lib/entry-points.js
+++ b/lib/entry-points.js
@@ -144518,19 +144518,41 @@ function optionalOrNull(validator) {
   };
 }
 function validateSchema(schema, obj) {
+  const result = checkSchema(schema, obj, { failFast: true });
+  return result.valid;
+}
+function checkSchema(schema, obj, options = {}, path29 = "") {
+  const result = { valid: true, unknownKeys: [] };
+  const inputKeys = new Set(Object.keys(obj));
   for (const [key, validator] of Object.entries(schema)) {
     const hasKey = key in obj;
     if (validator.required && !hasKey) {
-      return false;
+      result.valid = false;
+      if (options.failFast) {
+        return result;
+      }
+      continue;
     }
     if (validator.required && (obj[key] === void 0 || obj[key] === null)) {
-      return false;
+      result.valid = false;
+      if (options.failFast) {
+        return result;
+      }
+      continue;
     }
     if (hasKey && !validator.validate(obj[key])) {
-      return false;
+      result.valid = false;
+      if (options.failFast) {
+        return result;
+      }
+      continue;
     }
+    inputKeys.delete(key);
   }
-  return true;
+  for (const remainingKey of inputKeys) {
+    result.unknownKeys.push(`${path29}${remainingKey}`);
+  }
+  return result;
 }
 
 // src/util.ts
diff --git a/src/json/index.test.ts b/src/json/index.test.ts
index eb259c757..5234872e5 100644
--- a/src/json/index.test.ts
+++ b/src/json/index.test.ts
@@ -67,3 +67,13 @@ test("validateSchema - optional properties are optional", async (t) => {
   t.true(json.validateSchema(optionalSchema, { optionalKey: "" }));
   t.true(json.validateSchema(optionalSchema, { optionalKey: "foo" }));
 });
+
+test("validateSchema - checkSchema reports unknown keys", async (t) => {
+  const result = json.checkSchema(testSchema, {
+    requiredKey: "foo",
+    extraKey: "bar",
+  });
+
+  t.true(result.valid);
+  t.deepEqual(result.unknownKeys, ["extraKey"]);
+});
diff --git a/src/json/index.ts b/src/json/index.ts
index a55de5b58..d0a8edb51 100644
--- a/src/json/index.ts
+++ b/src/json/index.ts
@@ -121,24 +121,72 @@ export function validateSchema<S extends Schema>(
   schema: S,
   obj: UnvalidatedObject<any>,
 ): obj is FromSchema<S> {
+  const result = checkSchema(schema, obj, { failFast: true });
+  return result.valid;
+}
+
+export interface CheckSchemaOptions {
+  /** Whether to stop validation after the first error. */
+  failFast?: boolean;
+}
+
+export interface CheckSchemaResult {
+  /** Whether the `obj` satisfies the schema. */
+  valid: boolean;
+  /** Unknown keys that were found during validation. */
+  unknownKeys: string[];
+}
+
+export function checkSchema<S extends Schema>(
+  schema: S,
+  obj: UnvalidatedObject<any>,
+  options: CheckSchemaOptions = {},
+  path: string = "",
+): CheckSchemaResult {
+  const result: CheckSchemaResult = { valid: true, unknownKeys: [] };
+  const inputKeys = new Set(Object.keys(obj));
+
   for (const [key, validator] of Object.entries(schema)) {
     const hasKey = key in obj;
 
     // If the property is required, but absent, fail.
     if (validator.required && !hasKey) {
-      return false;
+      result.valid = false;
+
+      if (options.failFast) {
+        return result;
+      }
+      continue;
     }
 
     // If the property is required, but undefined or null, fail.
     if (validator.required && (obj[key] === undefined || obj[key] === null)) {
-      return false;
+      result.valid = false;
+
+      if (options.failFast) {
+        return result;
+      }
+      continue;
     }
 
     // If the property is present, validate it.
     if (hasKey && !validator.validate(obj[key])) {
-      return false;
+      result.valid = false;
+
+      if (options.failFast) {
+        return result;
+      }
+      continue;
     }
+
+    // If we reach this point, the key has been successfully validated.
+    inputKeys.delete(key);
   }
 
-  return true;
+  // If there are any remaining keys in `inputKeys`, add them to `unknownKeys`.
+  for (const remainingKey of inputKeys) {
+    result.unknownKeys.push(`${path}${remainingKey}`);
+  }
+
+  return result;
 }