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Build a Chat Agent with a Graph

Create an agent whose graph is a simple HumanMessageGuardrail → Generate chain, send a message, and get a streamed reply.

Prerequisites

Steps

from tryll_client import GraphDescription, NodeType

# 1. Build the graph.
graph = (
    GraphDescription()
    .add_node("guard",  NodeType.HumanMessageGuardrail)
    .add_node("answer", NodeType.Generate)
    .wire("guard",  "triggered",     "END")      # drop jailbreaks silently
    .wire("guard",  "not_triggered", "answer")
    .wire("answer", "default",       "END")
    .set_start_node("guard")
    .set_default_model_name("My Local Model")
)

# 2. Create the agent.
agent = client.create_agent(graph)

# 3. Send a message. send_message blocks and returns the full reply.
reply = agent.send_message("Hello!")
print(reply)

#include <tryll/TryllClient.h>

namespace TC = Tryll::Client;

TC::GraphDescription graph;
graph.AddNode("guard",  TC::NodeType::HumanMessageGuardrail)
     .AddNode("answer", TC::NodeType::Generate)
     .Wire("guard",  "triggered",     "END")
     .Wire("guard",  "not_triggered", "answer")
     .Wire("answer", "default",       "END")
     .SetStartNode("guard")
     .SetDefaultModelName("My Local Model");

auto agent = client.CreateAgent(graph);

// Stream tokens to stdout as they arrive.
agent.SendText("Hello!",
    [](std::string_view text, bool /*isDelta*/, bool /*isFinal*/)
    { std::cout << text << std::flush; });
  1. Add a UTryllAgentComponent to your actor.
  2. In the Details panel, edit Graph on the component, or reference a UTryllWorkflowAsset you authored in the Content Browser. Wire guard.triggered → END, guard.not_triggered → answer, answer.default → END.
  3. In Blueprint:
    • Bind On Agent Ready to a handler that calls Send Message.
    • Bind On Answer Text to append each chunk to a UI text block.
    • Bind On Turn Complete to flip the "typing" indicator off.

Verify it worked

Server-side, at info log level, one turn produces:

[info] Agent 7: turn starting
[info] Node guard: not_triggered
[info] Node answer: default
[info] Agent 7: turn complete (Success, tokens=128)

Client-side, Python returns the full reply string from send_message, while C++ and Unreal see each streamed chunk arrive in the SendText callback / OnAnswerText delegate, terminated by a TurnComplete with status Success.

Common pitfalls

  • "Model not found" (error 4002) — either the name is wrong, or the model is not in models.json. Double-check with client.list_models().
  • "Graph validation failed" (error 3003) — the most common cause is an unwired exit route. Every exit of every node must point somewhere.
  • Silent nothing after SendMessage. Check that the start node is not an always-END branch (e.g., guardrail that matches everything). The server log will show which route was taken.