send errors back to LLM

Author: ezynda3

internal/agent/agent.go

@@ -2,11 +2,13 @@ package agent
 
 import (
 	"context"
+	"encoding/json"
 	"fmt"
 
 	"github.com/cloudwego/eino/components/model"
 	"github.com/cloudwego/eino/components/tool"
 	"github.com/cloudwego/eino/schema"
+	"github.com/mark3labs/mcp-go/mcp"
 	"github.com/mark3labs/mcphost/internal/config"
 	"github.com/mark3labs/mcphost/internal/models"
 	"github.com/mark3labs/mcphost/internal/tools"
@@ -154,11 +156,20 @@ func (a *Agent) GenerateWithLoop(ctx context.Context, messages []*schema.Message
 							onToolResult(toolCall.Function.Name, toolCall.Function.Arguments, errorMsg, true)
 						}
 					} else {
+						// Check if this is an MCP tool response with an error
+						isError := false
+						if output != "" {
+							var mcpResult mcp.CallToolResult
+							if err := json.Unmarshal([]byte(output), &mcpResult); err == nil && mcpResult.IsError {
+								isError = true
+							}
+						}
+
 						toolMessage := schema.ToolMessage(output, toolCall.ID)
 						workingMessages = append(workingMessages, toolMessage)
 
 						if onToolResult != nil {
-							onToolResult(toolCall.Function.Name, toolCall.Function.Arguments, output, false)
+							onToolResult(toolCall.Function.Name, toolCall.Function.Arguments, output, isError)
 						}
 					}
 				} else {

internal/tools/mcp.go

@@ -154,9 +154,11 @@ func (t *mcpToolImpl) InvokableRun(ctx context.Context, argumentsInJSON string,
 	if err != nil {
 		return "", fmt.Errorf("failed to marshal mcp tool result: %w", err)
 	}
-	if result.IsError {
-		return "", fmt.Errorf("failed to call mcp tool, mcp server return error: %s", marshaledResult)
-	}
+
+	// If the MCP server returned an error, we still return the error content as the response
+	// to the LLM so it can see what went wrong. The error will be shown to the user via
+	// the UI callbacks, but the LLM needs to see the actual error details to continue
+	// the conversation appropriately.
 	return marshaledResult, nil
 }