patterns

Langroid Patterns

Instructions

Below is an INDEX of design patterns organized by category. Each item describes WHAT you might want to implement, followed by a REFERENCE to a document with a complete code example.

Scan this index to find patterns matching your needs, then consult the corresponding document.

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Agent & Task Basics

1. Task Returns Tool Directly

   Create a Langroid Agent equipped with a single Tool (a ToolMessage), and wrap it in a Task so that running the task returns that ToolMessage directly. Use this pattern when you want a simple LLM agent that returns a structured response.

   • Reference: ./task-return-tool.md

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Tool Handlers

1. Stateful Handler on Agent

   Define a STATEFUL tool handler as a METHOD on the agent (not inside the ToolMessage). Use this pattern when: (a) the tool handler needs to execute external operations (API calls, database queries, file I/O), (b) you need to track state across retries (e.g., failure counter), (c) the handler needs access to agent-level resources (connections, configs), or (d) you want Langroid to automatically loop errors back to the LLM for self-correction. The method name must match the request field of the ToolMessage. Return a string for errors (LLM sees it and can retry), or DoneTool(content=result) to terminate successfully.

   • Reference: ./agent-tool-handler-with-state.md

2. Handler with Validation

   Validate tool output against agent state before accepting it. Use this pattern when: (a) the LLM's tool output must preserve certain content from the input (e.g., placeholders, required fields), (b) you want automatic retry if validation fails, (c) you need to compare tool output against context the LLM received. Define a handler method on a custom agent class that stores the input context as state, validates the tool output, and returns an error string for retry or AgentDoneTool for success (note: use AgentDoneTool, NOT DoneTool). Use done_sequences=["T[ToolName], A"] so the handler runs before task termination.