diff --git a/packages/evaluator-sdk-py/src/agentevals_evaluator_sdk/__init__.py b/packages/evaluator-sdk-py/src/agentevals_evaluator_sdk/__init__.py
index 225e8a8..deec275 100644
--- a/packages/evaluator-sdk-py/src/agentevals_evaluator_sdk/__init__.py
+++ b/packages/evaluator-sdk-py/src/agentevals_evaluator_sdk/__init__.py
@@ -24,6 +24,7 @@ def my_evaluator(input: EvalInput) -> EvalResult:
 from .types import (
     EvalInput,
     EvalResult,
+    EvalStatus,
     IntermediateStepData,
     InvocationData,
     ToolCallData,
@@ -34,6 +35,7 @@ def my_evaluator(input: EvalInput) -> EvalResult:
     "evaluator",
     "EvalInput",
     "EvalResult",
+    "EvalStatus",
     "IntermediateStepData",
     "InvocationData",
     "ToolCallData",
diff --git a/packages/evaluator-sdk-py/src/agentevals_evaluator_sdk/types.py b/packages/evaluator-sdk-py/src/agentevals_evaluator_sdk/types.py
index 101026d..51974b1 100644
--- a/packages/evaluator-sdk-py/src/agentevals_evaluator_sdk/types.py
+++ b/packages/evaluator-sdk-py/src/agentevals_evaluator_sdk/types.py
@@ -7,6 +7,7 @@
 
 from __future__ import annotations
 
+from enum import Enum
 from typing import Any, Optional
 
 from pydantic import BaseModel, Field
@@ -63,13 +64,21 @@ class EvalInput(BaseModel):
     expected_invocations: Optional[list[InvocationData]] = None
 
 
+class EvalStatus(str, Enum):
+    """Wire JSON uses the string values (stable protocol with agentevals CLI)."""
+
+    PASSED = "PASSED"
+    FAILED = "FAILED"
+    NOT_EVALUATED = "NOT_EVALUATED"
+
+
 class EvalResult(BaseModel):
     """Output payload expected from a custom evaluator script/container on stdout."""
 
     score: float = Field(ge=0.0, le=1.0)
-    status: Optional[str] = Field(
+    status: Optional[EvalStatus] = Field(
         default=None,
-        description='One of "PASSED", "FAILED", "NOT_EVALUATED". Derived from score vs threshold if omitted.',
+        description="One of EvalStatus.PASSED, EvalStatus.FAILED, EvalStatus.NOT_EVALUATED. Derived from score vs threshold if omitted.",
     )
     per_invocation_scores: list[Optional[float]] = Field(default_factory=list)
     details: Optional[dict[str, Any]] = None
diff --git a/src/agentevals/_protocol.py b/src/agentevals/_protocol.py
index add1484..4508490 100644
--- a/src/agentevals/_protocol.py
+++ b/src/agentevals/_protocol.py
@@ -14,6 +14,7 @@
 
 from __future__ import annotations
 
+from enum import Enum
 from typing import Any, Optional
 
 from pydantic import BaseModel, Field
@@ -62,13 +63,21 @@ class EvalInput(BaseModel):
     expected_invocations: Optional[list[InvocationData]] = None
 
 
+class EvalStatus(str, Enum):
+    """Allowed ``status`` values on the evaluator JSON wire format (matches evaluator-sdk)."""
+
+    PASSED = "PASSED"
+    FAILED = "FAILED"
+    NOT_EVALUATED = "NOT_EVALUATED"
+
+
 class EvalResult(BaseModel):
     """Output payload expected from a custom evaluator on stdout."""
 
     score: float = Field(ge=0.0, le=1.0)
-    status: Optional[str] = Field(
+    status: Optional[EvalStatus] = Field(
         default=None,
-        description='One of "PASSED", "FAILED", "NOT_EVALUATED". Derived from score vs threshold if omitted.',
+        description="Derived from score vs threshold if omitted.",
     )
     per_invocation_scores: list[Optional[float]] = Field(default_factory=list)
     details: Optional[dict[str, Any]] = None
diff --git a/tests/test_protocol.py b/tests/test_protocol.py
new file mode 100644
index 0000000..8c0f14e
--- /dev/null
+++ b/tests/test_protocol.py
@@ -0,0 +1,25 @@
+"""Tests for the custom evaluator JSON protocol models."""
+
+import pytest
+from pydantic import ValidationError
+
+from agentevals._protocol import EvalResult, EvalStatus
+
+
+def test_eval_result_accepts_valid_status_strings() -> None:
+    raw = '{"score":1.0,"status":"PASSED","per_invocation_scores":[1.0]}'
+    r = EvalResult.model_validate_json(raw)
+    assert r.status == EvalStatus.PASSED
+    assert r.score == 1.0
+
+
+def test_eval_result_rejects_invalid_status() -> None:
+    raw = '{"score":1.0,"status":"MAYBE","per_invocation_scores":[]}'
+    with pytest.raises(ValidationError):
+        EvalResult.model_validate_json(raw)
+
+
+def test_eval_result_omitted_status_ok() -> None:
+    raw = '{"score":0.5,"per_invocation_scores":[]}'
+    r = EvalResult.model_validate_json(raw)
+    assert r.status is None