diff --git a/app-instance/backend/beaver/skills/learning/__init__.py b/app-instance/backend/beaver/skills/learning/__init__.py
index 1a4f5f3..4bd4cd8 100644
--- a/app-instance/backend/beaver/skills/learning/__init__.py
+++ b/app-instance/backend/beaver/skills/learning/__init__.py
@@ -13,6 +13,7 @@ from .pipeline import SkillLearningPipelineService
 from .preservation import check_preservation
 from .replay import ReplayToolExecutor, ReplayToolPolicy, classify_tool_mode
 from .service import RunReceiptContext, SkillLearningService
+from .surrogate import SurrogateToolEvaluator
 from .synthesizer import SkillDraftSynthesizer
 from .worker import SkillLearningWorker, SkillLearningWorkerConfig, SkillLearningWorkerResult
 
@@ -31,6 +32,7 @@ __all__ = [
     "ReplayToolExecutor",
     "ReplayToolPolicy",
     "classify_tool_mode",
+    "SurrogateToolEvaluator",
     "SkillDraftSynthesizer",
     "SkillLearningService",
     "SkillLearningWorker",
diff --git a/app-instance/backend/beaver/skills/learning/surrogate.py b/app-instance/backend/beaver/skills/learning/surrogate.py
new file mode 100644
index 0000000..ab2d3ff
--- /dev/null
+++ b/app-instance/backend/beaver/skills/learning/surrogate.py
@@ -0,0 +1,53 @@
+"""Surrogate evaluation for replay tool calls that cannot execute safely."""
+
+from __future__ import annotations
+
+from typing import Any
+
+
+class SurrogateToolEvaluator:
+    async def evaluate(self, *, task_text: str, baseline: dict[str, Any], candidate: dict[str, Any]) -> dict[str, Any]:
+        baseline_score = _score_arm(task_text, baseline)
+        candidate_score = _score_arm(task_text, candidate)
+        surrogate_count = _mode_count(baseline, "surrogate") + _mode_count(candidate, "surrogate")
+        blocked_count = _mode_count(baseline, "blocked") + _mode_count(candidate, "blocked")
+        confidence = "low" if blocked_count else ("medium" if surrogate_count <= 2 else "low")
+        return {
+            "baseline_score": baseline_score,
+            "candidate_score": candidate_score,
+            "delta": round(candidate_score - baseline_score, 4),
+            "surrogate_tool_count": surrogate_count,
+            "blocked_tool_count": blocked_count,
+            "confidence": confidence,
+            "notes": [
+                "Surrogate score is based on intended tool calls, schemas, arguments, and task relevance.",
+            ],
+        }
+
+
+def _score_arm(task_text: str, arm: dict[str, Any]) -> float:
+    calls = [item for item in arm.get("tool_calls") or [] if isinstance(item, dict)]
+    if not calls:
+        return 0.5
+    scores = [_score_call(task_text, call) for call in calls]
+    return round(sum(scores) / len(scores), 4)
+
+
+def _score_call(task_text: str, call: dict[str, Any]) -> float:
+    if call.get("mode") == "blocked":
+        return 0.2
+    if call.get("mode") == "executed":
+        result = call.get("result") if isinstance(call.get("result"), dict) else {}
+        return 0.85 if result.get("success") is not False else 0.35
+    arguments = dict(call.get("arguments") or {})
+    if not arguments:
+        return 0.45
+    non_empty = sum(1 for value in arguments.values() if str(value).strip())
+    completeness = non_empty / max(1, len(arguments))
+    argument_text = " ".join(str(value).lower() for value in arguments.values())
+    relevance = 0.15 if any(token and token in argument_text for token in task_text.lower().split()[:16]) else 0.0
+    return round(min(0.9, 0.5 + 0.3 * completeness + relevance), 4)
+
+
+def _mode_count(arm: dict[str, Any], mode: str) -> int:
+    return sum(1 for item in arm.get("tool_calls") or [] if isinstance(item, dict) and item.get("mode") == mode)
diff --git a/app-instance/backend/tests/unit/test_skill_learning_surrogate.py b/app-instance/backend/tests/unit/test_skill_learning_surrogate.py
new file mode 100644
index 0000000..47d6847
--- /dev/null
+++ b/app-instance/backend/tests/unit/test_skill_learning_surrogate.py
@@ -0,0 +1,31 @@
+from __future__ import annotations
+
+import asyncio
+
+from beaver.skills.learning.surrogate import SurrogateToolEvaluator
+
+
+def test_surrogate_scores_complete_candidate_higher_than_missing_baseline() -> None:
+    evaluator = SurrogateToolEvaluator()
+    baseline = {
+        "arm": "baseline",
+        "tool_calls": [
+            {"tool_name": "mcp_outlook_send_email", "mode": "surrogate", "arguments": {"to": "", "subject": ""}},
+        ],
+    }
+    candidate = {
+        "arm": "candidate",
+        "tool_calls": [
+            {
+                "tool_name": "mcp_outlook_send_email",
+                "mode": "surrogate",
+                "arguments": {"to": "ada@example.com", "subject": "Status", "body": "Done"},
+            },
+        ],
+    }
+
+    result = asyncio.run(evaluator.evaluate(task_text="Send a status email to Ada.", baseline=baseline, candidate=candidate))
+
+    assert result["candidate_score"] > result["baseline_score"]
+    assert result["surrogate_tool_count"] == 2
+    assert result["confidence"] in {"low", "medium"}