Data Flow Between Nodes

Multi-agent workflows pass data through graph inputs and node outputs. Each agent node returns a dictionary of outputs. Downstream nodes and edge conditions read values from that dictionary.

For predictable workflows, define the contract between nodes explicitly with WithOutputKey(...), WithInputKey(...), WithInputTemplate(...), or structured outputs.

Multi-agent workflows do not expose port-level routing in the agent workflow builder. Model agent-to-agent data flow with named output keys, input keys, input templates, structured outputs, and route conditions.

String Output

String mode is the default. HPD buffers the child agent's streamed text and writes it to answer unless you set an output key:

.AddAgent("research", researchConfig, node => node.WithOutputKey("research"))
.AddAgent("write", writerConfig, node => node.WithInputKey("research"))
.From("research").To("write")

In this workflow, the first node writes:

{
  "research": "..."
}

The second node reads research as its input.

Input Resolution

If a node does not set an input key or template, HPD chooses an input using this order:

1. InputTemplate
2. InputKey
3. shared.input
4. question, input, message, query, prompt
5. namespaced semantic keys such as research.input
6. original workflow input
7. first non-empty upstream string that is not shared.*
8. empty string

The sharp edge is shared.input: it is the original workflow input, and it is available to all nodes. A downstream node can keep seeing the original request instead of a previous node's output unless you explicitly wire the data contract.

Input Templates

Use WithInputTemplate(...) when a node needs more than one value:

.AddAgent("write", writerConfig, node => node.WithInputTemplate("""
User request:
{{shared.input}}

Research:
{{research}}

Risks:
{{risks}}
"""))

The template renderer performs simple replacement over the graph input bag. Treat it as placeholder replacement, not full Handlebars.

Structured Output

Structured mode asks the child agent for a structured result and flattens non-null public properties into lowercase output keys.

public sealed record AnalysisResult(
    string Sentiment,
    double Confidence,
    string Recommendation);

var workflow = await AgentWorkflow.Create()
    .AddAgent("analyze", analyzerConfig, node => node.StructuredOutput<AnalysisResult>())
    .AddAgent("approve", approvalConfig)
    .From("analyze").To("approve").WhenGreaterThan("confidence", 0.8)
    .BuildAsync();

If the model returns AnalysisResult, downstream routing sees keys such as:

{
  "sentiment": "positive",
  "confidence": 0.91,
  "recommendation": "ship",
  "result": {}
}

Property names are lowercased. Route on confidence, not Confidence.

Union Output

Union mode asks the child agent to return one of several result types. HPD flattens the result and adds matched_type.

public sealed record MathRoute(string Question);
public sealed record ResearchRoute(string Topic);
public sealed record GeneralRoute(string Request);

var workflow = await AgentWorkflow.Create()
    .AddAgent("classify", classifierConfig, node =>
        node.UnionOutput<MathRoute, ResearchRoute, GeneralRoute>())
    .AddAgent("solve_math", mathConfig)
    .AddAgent("research", researchConfig)
    .AddAgent("answer", generalConfig)
    .From("classify").RouteByType()
        .When<MathRoute>("solve_math")
        .When<ResearchRoute>("research")
        .When<GeneralRoute>("answer")
    .BuildAsync();

RouteByType() matches matched_type against typeof(T).Name.

Child Agent Run Config

Node options can also affect each child agent run:

• WithInstructions(...) appends node-specific system instructions.
• WithTimeout(...) sets the child run timeout.
• WithContext(...) provides runtime context instances for tool harnesses.
• structured and union modes set structured-output options.
• handoff mode injects generated handoff tools and requires a handoff tool call.

Retry, graph timeout, and edge routing are graph-level concerns, not ordinary chat options.

Related Pages

• Build A Multi-Agent Workflow
• Routing And Handoffs
• Workflow Events