diff --git a/ringer.py b/ringer.py
index 0dca41b..b22d083 100755
--- a/ringer.py
+++ b/ringer.py
@@ -127,6 +127,30 @@ def process_name(self) -> str:
         return Path(self.bin).name or self.name
 
 
+@dataclass(frozen=True)
+class EngineBinDiagnostic:
+    engine: str
+    config_key: str
+    value: str
+    path_value: str | None
+    path_was_set: bool
+    default_search_path: str = field(default_factory=lambda: os.defpath)
+
+    @property
+    def searched_path_display(self) -> str:
+        if not self.path_was_set:
+            return f"<unset> (shutil default: {self.default_search_path!r})"
+        if self.path_value == "":
+            return "<empty>"
+        return repr(self.path_value)
+
+    def warning(self) -> str:
+        return (
+            f"ringer.py: warning: {self.config_key} = {self.value!r} is not resolvable; "
+            f"searched PATH: {self.searched_path_display}"
+        )
+
+
 @dataclass(frozen=True)
 class PostgresEvalConfig:
     env_file: Path
@@ -428,6 +452,7 @@ class AppConfig:
     artifact: ArtifactConfig
     steering: SteeringConfig = field(default_factory=SteeringConfig)
     update: UpdateConfig = field(default_factory=UpdateConfig)
+    engine_bin_diagnostics: tuple[EngineBinDiagnostic, ...] = ()
 
     @classmethod
     def load(cls, path: Path | None = None) -> "AppConfig":
@@ -452,7 +477,12 @@ def load(cls, path: Path | None = None) -> "AppConfig":
         hud_app_path = optional_path(data.get("hud_app_path"))
         allow_full_access = bool(data.get("allow_full_access", False))
         eval_config = load_eval_config(data.get("eval"), state_dir)
-        engines = load_engines(data.get("engines"))
+        raw_engines = data.get("engines")
+        engines = load_engines(raw_engines)
+        engine_bin_diagnostics = collect_engine_bin_diagnostics(
+            engines,
+            engine_names=configured_engine_names(raw_engines),
+        )
         artifact_config = load_artifact_config(data.get("artifact"), state_dir)
         update_config = load_update_config(data.get("update"))
         try:
@@ -474,6 +504,7 @@ def load(cls, path: Path | None = None) -> "AppConfig":
             artifact=artifact_config,
             steering=steering_config,
             update=update_config,
+            engine_bin_diagnostics=engine_bin_diagnostics,
         )
 
 
@@ -926,6 +957,71 @@ def load_hud_port(raw: Any) -> int:
     return port
 
 
+def configured_engine_names(raw: Any) -> tuple[str, ...]:
+    if not isinstance(raw, dict):
+        return ()
+    names: list[str] = []
+    for name in raw:
+        clean = str(name).strip()
+        if clean:
+            names.append(clean)
+    return tuple(names)
+
+
+def has_path_separator(value: str) -> bool:
+    separators = tuple(sep for sep in (os.sep, os.altsep) if sep)
+    return any(sep in value for sep in separators)
+
+
+def collect_engine_bin_diagnostics(
+    engines: dict[str, EngineConfig],
+    *,
+    engine_names: Iterable[str] | None = None,
+    path_value: str | None = None,
+    path_was_set: bool | None = None,
+) -> tuple[EngineBinDiagnostic, ...]:
+    if path_was_set is None:
+        path_was_set = "PATH" in os.environ
+    if path_value is None and path_was_set:
+        path_value = os.environ.get("PATH", "")
+    search_path = path_value if path_was_set else os.defpath
+    names = tuple(engine_names) if engine_names is not None else tuple(engines)
+
+    diagnostics: list[EngineBinDiagnostic] = []
+    for name in names:
+        engine = engines.get(name)
+        if engine is None:
+            continue
+        bin_value = engine.bin
+        if has_path_separator(bin_value):
+            continue
+        if shutil.which(bin_value, path=search_path) is not None:
+            continue
+        diagnostics.append(
+            EngineBinDiagnostic(
+                engine=name,
+                config_key=f"engines.{name}.bin",
+                value=bin_value,
+                path_value=path_value,
+                path_was_set=path_was_set,
+            )
+        )
+    return tuple(diagnostics)
+
+
+def print_engine_bin_diagnostics(config: AppConfig) -> None:
+    for diagnostic in config.engine_bin_diagnostics:
+        print(diagnostic.warning(), file=sys.stderr)
+
+
+def print_engine_bin_diagnostics_if_config_loads(path: Path | None) -> None:
+    try:
+        config = AppConfig.load(path)
+    except Exception:
+        return
+    print_engine_bin_diagnostics(config)
+
+
 def load_engines(raw: Any) -> dict[str, EngineConfig]:
     engines: dict[str, EngineConfig] = {DEFAULT_ENGINE_NAME: built_in_codex_engine()}
     if raw is None:
@@ -10053,6 +10149,7 @@ def main(argv: list[str] | None = None) -> int:
 
         if args.command == "lint":
             manifest = Manifest.from_path(args.manifest)
+            print_engine_bin_diagnostics_if_config_loads(args.config)
             findings = lint_manifest(
                 manifest,
                 allow_noncanonical_route=args.allow_noncanonical_route,
@@ -10067,6 +10164,7 @@ def main(argv: list[str] | None = None) -> int:
             return run_catalog_command(args)
 
         config = AppConfig.load(args.config)
+        print_engine_bin_diagnostics(config)
         if args.command == "db":
             return run_db_command(config, args)
         if args.command == "models":
diff --git a/tests/test_engine_bin_warning.py b/tests/test_engine_bin_warning.py
new file mode 100644
index 0000000..05a07f7
--- /dev/null
+++ b/tests/test_engine_bin_warning.py
@@ -0,0 +1,228 @@
+from __future__ import annotations
+
+import contextlib
+import io
+import json
+import os
+import sys
+import tempfile
+import unittest
+from dataclasses import FrozenInstanceError
+from pathlib import Path
+from unittest import mock
+
+ROOT = Path(__file__).resolve().parents[1]
+sys.path.insert(0, str(ROOT))
+
+import ringer  # noqa: E402
+
+
+LONG_SPEC = (
+    "Create result.txt in the task directory with a clear success marker, keep the work scoped, "
+    "and make any failure easy to diagnose from the check output."
+)
+GOOD_CHECK = "test -s result.txt || { echo 'missing result.txt'; exit 1; }"
+MISSING_BIN = "ringer-definitely-missing-engine-bin"
+
+
+def toml_string(value: object) -> str:
+    return json.dumps(str(value))
+
+
+class EngineBinWarningTests(unittest.TestCase):
+    def setUp(self) -> None:
+        self.tmp = tempfile.TemporaryDirectory(prefix="ringer-engine-bin-")
+        self.root = Path(self.tmp.name)
+        self.config_path = self.root / "config.toml"
+        self.manifest_path = self.root / "manifest.json"
+        self.path_dir = self.root / "path"
+        self.path_dir.mkdir()
+
+    def tearDown(self) -> None:
+        self.tmp.cleanup()
+
+    def engine(self, name: str, bin_value: str) -> ringer.EngineConfig:
+        return ringer.EngineConfig(
+            name=name,
+            bin=bin_value,
+            args_template=("{spec}",),
+            full_access_args=(),
+            sandbox_args=(),
+            token_regex=None,
+        )
+
+    def write_config(self, engines: dict[str, str]) -> None:
+        lines = [
+            f"state_dir = {toml_string(self.root / 'state')}",
+            "",
+            "[eval]",
+            f"jsonl_path = {toml_string(self.root / 'runs.jsonl')}",
+            "",
+        ]
+        for name, bin_value in engines.items():
+            lines.extend(
+                [
+                    f"[engines.{name}]",
+                    f"bin = {toml_string(bin_value)}",
+                    'args_template = ["{spec}"]',
+                    "sandbox_args = []",
+                    "full_access_args = []",
+                    "",
+                ]
+            )
+        self.config_path.write_text("\n".join(lines), encoding="utf-8")
+
+    def write_manifest(self, *, engine: str = "worker", clean: bool = True) -> Path:
+        task = {
+            "key": "task-one",
+            "engine": engine,
+            "spec": LONG_SPEC if clean else "too short",
+            "check": GOOD_CHECK,
+            "expect_files": ["result.txt"],
+            "verified": "result.txt exists and is non-empty.",
+            "task_type": "code-feature",
+        }
+        data = {
+            "run_name": "engine-bin-warning-test",
+            "workdir": str(self.root / "work"),
+            "max_parallel": 1,
+            "tasks": [task],
+        }
+        self.manifest_path.write_text(json.dumps(data), encoding="utf-8")
+        return self.manifest_path
+
+    def run_main(self, argv: list[str]) -> tuple[int, str, str]:
+        stdout = io.StringIO()
+        stderr = io.StringIO()
+        with mock.patch.dict(
+            os.environ,
+            {"RINGER_NO_SELF_UPDATE": "1", "PATH": str(self.path_dir)},
+            clear=False,
+        ):
+            with contextlib.redirect_stdout(stdout), contextlib.redirect_stderr(stderr):
+                rc = ringer.main(argv)
+        return rc, stdout.getvalue(), stderr.getvalue()
+
+    def test_pure_diagnostics_are_immutable_and_name_key_value_and_path(self) -> None:
+        diagnostics = ringer.collect_engine_bin_diagnostics(
+            {"missing": self.engine("missing", MISSING_BIN)},
+            path_value=str(self.path_dir),
+            path_was_set=True,
+        )
+
+        self.assertEqual(1, len(diagnostics))
+        diagnostic = diagnostics[0]
+        self.assertEqual("engines.missing.bin", diagnostic.config_key)
+        self.assertEqual(MISSING_BIN, diagnostic.value)
+        self.assertIn("engines.missing.bin", diagnostic.warning())
+        self.assertIn(MISSING_BIN, diagnostic.warning())
+        self.assertIn(str(self.path_dir), diagnostic.warning())
+        with self.assertRaises(FrozenInstanceError):
+            diagnostic.value = "changed"  # type: ignore[misc]
+
+    def test_explicit_path_is_quiet_even_when_missing(self) -> None:
+        diagnostics = ringer.collect_engine_bin_diagnostics(
+            {"explicit": self.engine("explicit", str(self.root / "missing-tool"))},
+            path_value=str(self.path_dir),
+            path_was_set=True,
+        )
+
+        self.assertEqual((), diagnostics)
+
+    @unittest.skipIf(os.name == "nt", "POSIX executable-bit fixture")
+    def test_resolvable_bare_name_is_quiet(self) -> None:
+        executable = self.path_dir / "ok-engine"
+        executable.write_text("#!/bin/sh\nexit 0\n", encoding="utf-8")
+        executable.chmod(0o700)
+
+        diagnostics = ringer.collect_engine_bin_diagnostics(
+            {"ok": self.engine("ok", executable.name)},
+            path_value=str(self.path_dir),
+            path_was_set=True,
+        )
+
+        self.assertEqual((), diagnostics)
+
+    def test_unset_path_diagnostic_distinguishes_unset_from_empty(self) -> None:
+        diagnostics = ringer.collect_engine_bin_diagnostics(
+            {"missing": self.engine("missing", MISSING_BIN)},
+            path_was_set=False,
+        )
+
+        self.assertEqual(1, len(diagnostics))
+        warning = diagnostics[0].warning()
+        self.assertIn("searched PATH: <unset>", warning)
+        self.assertNotIn("<empty>", warning)
+
+    def test_lint_prints_warning_but_still_succeeds(self) -> None:
+        self.write_config({"missing": MISSING_BIN})
+        self.write_manifest(engine="missing", clean=True)
+
+        rc, stdout, stderr = self.run_main(
+            ["--config", str(self.config_path), "lint", str(self.manifest_path)]
+        )
+
+        self.assertEqual(0, rc)
+        self.assertIn("lint: clean", stdout)
+        self.assertIn("ringer.py: warning:", stderr)
+        self.assertIn("engines.missing.bin", stderr)
+        self.assertIn(MISSING_BIN, stderr)
+
+    def test_malformed_config_does_not_change_lint_result(self) -> None:
+        self.config_path.write_text("engines = 1\n", encoding="utf-8")
+        self.write_manifest(clean=False)
+
+        rc, stdout, stderr = self.run_main(
+            ["--config", str(self.config_path), "lint", str(self.manifest_path)]
+        )
+
+        self.assertEqual(1, rc)
+        self.assertIn("lint: task-one: spec is probably underspecified", stdout)
+        self.assertNotIn("config", stderr.lower())
+
+    def test_used_missing_engine_warns_before_fatal_preflight(self) -> None:
+        self.write_config({"missing": MISSING_BIN})
+        self.write_manifest(engine="missing", clean=True)
+
+        rc, _stdout, stderr = self.run_main(
+            [
+                "--config",
+                str(self.config_path),
+                "run",
+                str(self.manifest_path),
+                "--no-dashboard",
+                "--identity",
+                "test-runner",
+            ]
+        )
+
+        self.assertEqual(2, rc)
+        warning_index = stderr.index("ringer.py: warning:")
+        fatal_index = stderr.index("ringer.py: error: engine 'missing' binary not found")
+        self.assertLess(warning_index, fatal_index)
+
+    def test_unused_missing_engine_warns_without_fatal_preflight(self) -> None:
+        self.write_config({"worker": sys.executable, "unused": MISSING_BIN})
+        self.write_manifest(engine="worker", clean=True)
+
+        rc, stdout, stderr = self.run_main(
+            [
+                "--config",
+                str(self.config_path),
+                "run",
+                str(self.manifest_path),
+                "--no-dashboard",
+                "--identity",
+                "test-runner",
+                "--dry-run",
+            ]
+        )
+
+        self.assertEqual(0, rc)
+        self.assertIn("DRY RUN:", stdout)
+        self.assertIn("engines.unused.bin", stderr)
+        self.assertNotIn("binary not found", stderr)
+
+
+if __name__ == "__main__":
+    unittest.main(verbosity=2)