Tool Call Node

Node Configuration

{
  "nodeType": "MCPToolCall",
  "name": "analyzeDocument",
  "config": {
    "serverId": "bfai-document-ai",
    "toolName": "analyze-document",
    "inputMap": {
      "documentUrl": "$output.fetchDocument.url",
      "documentType": "$json.documentType",
      "extractionSchema": {
        "fields": ["invoiceNumber", "totalAmount", "currency", "vendorName"]
      }
    },
    "timeoutSeconds": 60,
    "retryCount": 2
  }
}

Configuration Fields

MCPToolCallExecutor — Implementation Pattern

public class MCPToolCallExecutor : BaseNodeExecutor<MCPToolCallSettings>
{
    private readonly IMCPServerRegistry _registry;
    private readonly IMCPClientFactory _clientFactory;
    private readonly IExpressionEvaluator _expr;

    public MCPToolCallExecutor(
        IMCPServerRegistry registry,
        IMCPClientFactory clientFactory,
        IExpressionEvaluator expr)
    {
        _registry = registry;
        _clientFactory = clientFactory;
        _expr = expr;
    }

    protected override async Task<NodeExecutionResult> ExecuteAsync(
        NodeExecutionContext ctx,
        MCPToolCallSettings settings,
        CancellationToken ct)
    {
        // 1. Resolve server definition
        if (!_registry.TryGetServer(settings.ServerId, out var serverDef))
            return NodeExecutionResult.Failure(
                $"MCP server '{settings.ServerId}' is not registered.");

        // 2. Evaluate inputMap expressions against current context
        var toolParameters = new Dictionary<string, object?>();
        foreach (var (paramName, expression) in settings.InputMap)
        {
            toolParameters[paramName] = expression is string s
                ? await _expr.EvaluateAsync(s, ctx, ct)
                : expression;   // literal object/array
        }

        // 3. Create authenticated MCP client (credentials resolved inside factory)
        await using var client = await _clientFactory.CreateClientAsync(serverDef, ct);

        // 4. Execute tool call with timeout
        using var cts = CancellationTokenSource.CreateLinkedTokenSource(ct);
        cts.CancelAfter(TimeSpan.FromSeconds(settings.TimeoutSeconds ?? serverDef.TimeoutSeconds));

        var callId = Guid.NewGuid().ToString("N");
        var callResult = await client.CallToolAsync(
            settings.ToolName,
            toolParameters,
            cts.Token);

        // 5. Return structured output
        return NodeExecutionResult.Success(new
        {
            result      = callResult.Content,
            toolName    = settings.ToolName,
            serverId    = settings.ServerId,
            callId      = callId,
            executedAt  = DateTimeOffset.UtcNow
        });
    }
}

Retry Behaviour

Retries apply only to transient failures: network errors, 429 Too Many Requests (with Retry-After respected), and 503/504 responses from the MCP server. Tool-level errors returned in the MCP response body (e.g., isError: true) are not retried — they surface immediately as node failure.