diff --git a/features/a2a_jsonrpc_wire_format.feature b/features/a2a_jsonrpc_wire_format.feature
index c1255857b..974bf83fc 100644
--- a/features/a2a_jsonrpc_wire_format.feature
+++ b/features/a2a_jsonrpc_wire_format.feature
@@ -189,3 +189,24 @@ Feature: A2A JSON-RPC 2.0 wire format compliance
     Given a wire-format facade with no services
     When I dispatch wire-format method "_cleveragents/health/check" with id "test-id-123" and params {}
     Then the wire-format response id should equal "test-id-123"
+
+  # -------------------------------------------------------------------
+  # A2aErrorDetail — JSON-RPC 2.0 field name compliance (issue #2745)
+  # -------------------------------------------------------------------
+
+  Scenario: A2aErrorDetail serialises with data field not details
+    Given an A2aErrorDetail with code "NOT_FOUND" and message "gone" and data {"id": "x"}
+    When I serialise the error detail to a dict
+    Then the error detail dict should contain key "data"
+    And the error detail dict should not contain key "details"
+
+  Scenario: A2aErrorDetail serialises with empty data by default
+    Given an A2aErrorDetail with code "ERR" and message "error" and no data
+    When I serialise the error detail to a dict
+    Then the error detail dict should contain key "data"
+    And the error detail dict should not contain key "details"
+
+  Scenario: A2aErrorDetail data field preserves payload values
+    Given an A2aErrorDetail with code "NOT_FOUND" and message "gone" and data {"plan_id": "abc123"}
+    When I serialise the error detail to a dict
+    Then the error detail data should contain key "plan_id"
diff --git a/features/steps/a2a_jsonrpc_wire_format_steps.py b/features/steps/a2a_jsonrpc_wire_format_steps.py
index b254d0873..7b3a42b88 100644
--- a/features/steps/a2a_jsonrpc_wire_format_steps.py
+++ b/features/steps/a2a_jsonrpc_wire_format_steps.py
@@ -350,5 +350,58 @@ def step_wire_response_id(context: Context, value: str) -> None:
     )
 
 
+# ---------------------------------------------------------------------------
+# A2aErrorDetail — JSON-RPC 2.0 field name compliance (issue #2745)
+# ---------------------------------------------------------------------------
+
+
+@given(
+    r'an A2aErrorDetail with code "(?P<code>[^"]+)" and message "(?P<msg>[^"]+)" and data (?P<data_json>.+)'
+)
+def step_create_error_detail_with_data(
+    context: Context, code: str, msg: str, data_json: str
+) -> None:
+    import json
+
+    data = json.loads(data_json)
+    context.error_detail = A2aErrorDetail(code=code, message=msg, data=data)
+
+
+@given(
+    r'an A2aErrorDetail with code "(?P<code>[^"]+)" and message "(?P<msg>[^"]+)" and no data'
+)
+def step_create_error_detail_no_data(context: Context, code: str, msg: str) -> None:
+    context.error_detail = A2aErrorDetail(code=code, message=msg)
+
+
+@when("I serialise the error detail to a dict")
+def step_serialise_error_detail(context: Context) -> None:
+    context.error_detail_dict = context.error_detail.model_dump()
+
+
+@then(r'the error detail dict should contain key "(?P<key>[^"]+)"')
+def step_error_detail_dict_has_key(context: Context, key: str) -> None:
+    assert key in context.error_detail_dict, (
+        f"Expected key '{key}' in error detail dict, got keys: "
+        f"{list(context.error_detail_dict.keys())}"
+    )
+
+
+@then(r'the error detail dict should not contain key "(?P<key>[^"]+)"')
+def step_error_detail_dict_no_key(context: Context, key: str) -> None:
+    assert key not in context.error_detail_dict, (
+        f"Expected key '{key}' NOT in error detail dict, but it was present with value: "
+        f"{context.error_detail_dict.get(key)!r}"
+    )
+
+
+@then(r'the error detail data should contain key "(?P<key>[^"]+)"')
+def step_error_detail_data_has_key(context: Context, key: str) -> None:
+    data = context.error_detail_dict.get("data", {})
+    assert key in data, (
+        f"Expected key '{key}' in error detail data, got keys: {list(data.keys())}"
+    )
+
+
 # Reset step matcher to parse (default) so subsequent step files are not affected
 use_step_matcher("parse")
diff --git a/src/cleveragents/a2a/models.py b/src/cleveragents/a2a/models.py
index 2d9c26fc7..a7f4f308b 100644
--- a/src/cleveragents/a2a/models.py
+++ b/src/cleveragents/a2a/models.py
@@ -68,7 +68,7 @@ class A2aErrorDetail(BaseModel):
 
     code: str
     message: str
-    details: dict[str, Any] = {}
+    data: dict[str, Any] = {}
 
     @field_validator("code", "message")
     @classmethod