@@ -1,6 +1,8 @@
+import difflib
+import warnings
 from collections.abc import Mapping
 from copy import deepcopy
-from typing import Any, Dict, Type, TypeVar
+from typing import Any, Dict, List, Optional, Type, TypeVar, get_args, get_origin
 
 import jsonref
 from pydantic import BaseModel
@@ -9,6 +11,93 @@
 RequestModelT = TypeVar("RequestModelT", bound=BaseModel)
 
 
+def _is_open(annotation: Any) -> bool:
+    """True for annotations whose mapping values are user-owned data."""
+    return (
+        annotation is Any
+        or annotation is dict
+        or get_origin(annotation) in (dict, Mapping, type)
+    )
+
+
+def _nested_model(annotation: Any) -> Optional[Type[BaseModel]]:
+    """Return the single request model wrapped by an annotation, if any.
+
+    Unwraps Optional, List and similar containers. Returns None for open
+    mappings and for unions of several models, which are left unchecked.
+    """
+    if isinstance(annotation, type) and issubclass(annotation, BaseModel):
+        return annotation
+    if _is_open(annotation):
+        return None
+
+    found = set()
+    for arg in get_args(annotation):
+        if _is_open(arg):
+            # The field also accepts an open mapping or a class, so a mapping
+            # value may be user-owned data (e.g. a JSON Schema). Skip it.
+            return None
+        nested = _nested_model(arg)
+        if nested is not None:
+            found.add(nested)
+    return found.pop() if len(found) == 1 else None
+
+
+def _unknown_keys(model: Type[BaseModel], data: Mapping, path: str) -> List[str]:
+    """List keys in a request mapping that the model would silently drop."""
+    if model.model_config.get("extra") in ("allow", "forbid"):
+        # "allow" keeps extra keys and "forbid" already raises on them.
+        return []
+
+    config = model.model_config
+    by_name = config.get("populate_by_name") or config.get("validate_by_name")
+    by_alias = config.get("validate_by_alias", True)
+
+    # Keys pydantic accepts on input, and the key to suggest for each field.
+    accepted = {}
+    preferred = {}
+    for field_name, field in model.model_fields.items():
+        inputs = []
+        if field.alias is None or by_name:
+            inputs.append(field_name)
+        if by_alias:
+            inputs += [a for a in (field.alias, field.validation_alias) if a]
+        inputs = [a for a in inputs if isinstance(a, str)]
+        for input_key in inputs:
+            accepted[input_key] = field
+        if inputs:
+            for wire_name in (field_name, field.serialization_alias):
+                if isinstance(wire_name, str) and wire_name not in accepted:
+                    preferred[wire_name] = inputs[0]
+
+    problems = []
+    for key, item in data.items():
+        if not isinstance(key, str):
+            continue
+        field = accepted.get(key)
+        if field is None:
+            if key in preferred:
+                hint = f"use '{preferred[key]}'"
+            else:
+                close = difflib.get_close_matches(key, list(accepted), n=1)
+                hint = f"did you mean '{close[0]}'?" if close else "unknown option"
+            problems.append(f"'{path}{key}' ({hint})")
+            continue
+
+        nested = _nested_model(field.annotation)
+        if nested is None:
+            continue
+        if isinstance(item, Mapping):
+            problems.extend(_unknown_keys(nested, item, f"{path}{key}."))
+        elif isinstance(item, (list, tuple)):
+            for index, element in enumerate(item):
+                if isinstance(element, Mapping):
+                    problems.extend(
+                        _unknown_keys(nested, element, f"{path}{key}[{index}].")
+                    )
+    return problems
+
+
 def coerce_request(
     value: Any,
     model: Type[RequestModelT],
@@ -19,6 +108,15 @@ def coerce_request(
     if isinstance(value, model):
         return value
     if isinstance(value, Mapping):
+        problems = _unknown_keys(model, value, "")
+        if problems:
+            warnings.warn(
+                f"{model.__name__} ignored unrecognized {name} keys: "
+                + ", ".join(problems)
+                + ". These options were not sent to the API.",
+                UserWarning,
+                stacklevel=4,
+            )
         return model.model_validate(dict(value))
     raise TypeError(
         f"{name} must be a {model.__name__} instance or mapping, "
 
@@ -0,0 +1,109 @@
+import warnings
+
+import pytest
+
+from hyperbrowser.client._request import dump_request
+from hyperbrowser.models import (
+    CreateSandboxParams,
+    CreateSessionParams,
+    StartBrowserUseTaskParams,
+    StartExtractJobParams,
+    StartScrapeJobParams,
+)
+
+
+def _dump_without_warnings(mapping, model):
+    with warnings.catch_warnings():
+        warnings.simplefilter("error")
+        return dump_request(mapping, model)
+
+
+def test_misspelled_key_warns_with_suggestion():
+    with pytest.warns(UserWarning) as record:
+        payload = dump_request(
+            {"use_stealth": True, "solve_captcha": True}, CreateSessionParams
+        )
+
+    message = str(record[0].message)
+    assert "'solve_captcha' (did you mean 'solve_captchas'?)" in message
+    assert "not sent to the API" in message
+    # Behaviour is unchanged apart from the warning.
+    assert payload["useStealth"] is True
+    assert payload["solveCaptchas"] is False
+
+
+def test_wire_name_key_warns_with_python_name():
+    with pytest.warns(UserWarning) as record:
+        payload = dump_request({"useStealth": True}, CreateSessionParams)
+
+    assert "'useStealth' (use 'use_stealth')" in str(record[0].message)
+    assert payload["useStealth"] is False
+
+
+def test_nested_request_model_keys_are_checked():
+    with pytest.warns(UserWarning) as record:
+        dump_request(
+            {
+                "url": "https://example.com",
+                "scrape_options": {"formats": ["markdown"], "only_main": True},
+            },
+            StartScrapeJobParams,
+        )
+
+    message = str(record[0].message)
+    assert "'scrape_options.only_main' (did you mean 'only_main_content'?)" in message
+
+
+def test_valid_mappings_do_not_warn():
+    _dump_without_warnings(
+        {
+            "use_stealth": True,
+            "solve_captchas": True,
+            "screen": {"width": 1920, "height": 1080},
+        },
+        CreateSessionParams,
+    )
+    _dump_without_warnings(
+        {
+            "url": "https://example.com",
+            "scrape_options": {"formats": ["markdown"], "only_main_content": True},
+        },
+        StartScrapeJobParams,
+    )
+
+
+def test_aliased_input_and_user_owned_mappings_do_not_warn():
+    _dump_without_warnings(
+        {
+            "urls": ["https://example.com"],
+            "schema": {"type": "object", "properties": {"anyKey": {}}},
+        },
+        StartExtractJobParams,
+    )
+    _dump_without_warnings(
+        {
+            "task": "log in",
+            "initial_actions": [{"custom_action": {"snake_case_key": None}}],
+        },
+        StartBrowserUseTaskParams,
+    )
+
+
+def test_open_mapping_fields_do_not_warn():
+    # Keys of a dict-typed field are user data, not option names.
+    _dump_without_warnings(
+        {"image_name": "node", "mounts": {"/workspace/cache": {"id": "vol_123"}}},
+        CreateSandboxParams,
+    )
+    # A field that accepts either a JSON Schema dict or a model class.
+    _dump_without_warnings(
+        {
+            "task": "extract",
+            "output_model_schema": {"type": "object", "$defs": {}, "x-custom": 1},
+        },
+        StartBrowserUseTaskParams,
+    )
+
+
+def test_legacy_model_instances_do_not_warn():
+    _dump_without_warnings(CreateSessionParams(use_stealth=True), CreateSessionParams)