Set ToolRetryError message

pydantic_ai_slim/pydantic_ai/exceptions.py

@@ -188,7 +188,23 @@ class ToolRetryError(Exception):
 
     def __init__(self, tool_retry: RetryPromptPart):
         self.tool_retry = tool_retry
-        super().__init__()
+        super().__init__(_format_tool_retry_message(tool_retry))
+
+
+def _format_tool_retry_message(tool_retry: RetryPromptPart) -> str:
+    """Format a human-readable error message for ToolRetryError."""
+    content = tool_retry.content
+    if isinstance(content, str):
+        return f"Tool '{tool_retry.tool_name}' failed: {content}"
+
+    # Format list of ErrorDetails in a human-readable way
+    error_count = len(content)
+    error_word = 'error' if error_count == 1 else 'errors'
+    lines = [f"Tool '{tool_retry.tool_name}' failed: {error_count} validation {error_word}"]
+    for error in content:
+        loc = '.'.join(str(loc) for loc in error['loc'])
+        lines.append(f'  {loc}: {error["msg"]}')
+    return '\n'.join(lines)
 
 
 class IncompleteToolCall(UnexpectedModelBehavior):

tests/test_exceptions.py

@@ -4,6 +4,7 @@
 from typing import Any
 
 import pytest
+from pydantic_core import ErrorDetails
 
 from pydantic_ai import ModelRetry
 from pydantic_ai.exceptions import (
@@ -13,10 +14,12 @@
     IncompleteToolCall,
     ModelAPIError,
     ModelHTTPError,
+    ToolRetryError,
     UnexpectedModelBehavior,
     UsageLimitExceeded,
     UserError,
 )
+from pydantic_ai.messages import RetryPromptPart
 
 
 @pytest.mark.parametrize(
@@ -32,6 +35,7 @@
         lambda: ModelAPIError('model', 'test message'),
         lambda: ModelHTTPError(500, 'model'),
         lambda: IncompleteToolCall('test'),
+        lambda: ToolRetryError(RetryPromptPart(content='test', tool_name='test')),
     ],
     ids=[
         'ModelRetry',
@@ -44,6 +48,7 @@
         'ModelAPIError',
         'ModelHTTPError',
         'IncompleteToolCall',
+        'ToolRetryError',
     ],
 )
 def test_exceptions_hashable(exc_factory: Callable[[], Any]):
@@ -59,3 +64,26 @@ def test_exceptions_hashable(exc_factory: Callable[[], Any]):
 
     assert exc in s
     assert d[exc] == 'value'
+
+
+def test_tool_retry_error_str():
+    """Test that ToolRetryError has a meaningful string representation."""
+    part = RetryPromptPart(content='Invalid query syntax', tool_name='sql_query')
+    error = ToolRetryError(part)
+    assert str(error) == "Tool 'sql_query' failed: Invalid query syntax"
+
+
+def test_tool_retry_error_str_with_error_details():
+    """Test that ToolRetryError handles list of ErrorDetails content."""
+    error_details: list[ErrorDetails] = [
+        {'type': 'missing', 'loc': ('field1',), 'msg': 'Field required', 'input': {}},
+        {'type': 'string_type', 'loc': ('field2',), 'msg': 'Input should be a valid string', 'input': 123},
+    ]
+    part = RetryPromptPart(content=error_details, tool_name='my_tool')
+    error = ToolRetryError(part)
+
+    expected = """\
+Tool 'my_tool' failed: 2 validation errors
+  field1: Field required
+  field2: Input should be a valid string"""
+    assert str(error) == expected