LangChain Tool Adapter

@rejelly/adapter-langchain provides fromLangChainTool for converting LangChain tools into Rejelly ToolDefinition, enabling reuse of the LangChain tool ecosystem.

For the receive-side contract of multimodal tool results, see Adapter · Multimodal Tool Results.

fromLangChainTool(tool, options?)

Basic usage:

import { createAgent, equipSystem, equipTool, promptAgent } from '@rejelly/core';
import { fromLangChainTool } from '@rejelly/adapter-langchain';
import { TavilySearchResults } from "@langchain/community/tools/tavily_search";
import { Calculator } from "@langchain/community/tools/calculator";

// Instantiate LangChain tools
const tavilyTool = new TavilySearchResults({ apiKey: "..." });
const calcTool = new Calculator();

const ResearchAgent = createAgent({
  id: 'researcher',
  model: openaiModel,
  handler: async (props) => {
    equipSystem('You are a researcher who excels at using tools.');

    // Directly convert and equip a LangChain tool
    equipTool(fromLangChainTool(tavilyTool));

    // Rename and customize description (optional)
    equipTool(fromLangChainTool(calcTool, {
      name: 'math_calculator',
      description: 'Must use this tool when precise numerical calculations are needed'
    }));

    const result = await promptAgent(ResultSchema);
    return result;
  }
});

fromLangChainTool interface:

/**
 * Adapts a LangChain tool to a Rejelly tool
 * @param tool - LangChain tool instance (compatible with StructuredTool and most tool implementations)
 * @param options - Optional override configuration
 */
function fromLangChainTool(
  tool: LangChainToolLike,
  options?: FromLangChainToolOptions
): ToolDefinition;

interface LangChainToolLike {
  name: string;
  description: string;
  schema?: z.ZodTypeAny;
  invoke?(input: any, options?: any): Promise<any>;
  call?: (input: any, options?: any): Promise<any>;
  func?: (input: any, options?: any): Promise<any>;
}

interface FromLangChainToolOptions {
  /** Override the tool name */
  name?: string;
  /** Override the tool description */
  description?: string;
}

How it works:

• Duck typing compatibility: Uses a minimal interface (LangChainToolLike) to avoid a hard dependency on the langchain library
• Schema extraction: Automatically extracts the Zod Schema from LangChain tools (modern tools typically expose it directly)
• Execution method adaptation: Supports invoke(), call(), func() and other execution methods (priority: invoke > call > func)
• AbortSignal injection: Automatically retrieves AbortSignal from AgentContext and passes it to LangChain tools
• Multimodal results: Content-block arrays returned by tools that include image blocks are converted to toolContent (see Adapter · Multimodal Tool Results); plain text / unrecognized results pass through unchanged
• Error handling: Friendly error wrapping that preserves the original error context

Notes:

• If a tool lacks a Zod Schema, it degrades to z.any() and prints a warning (this may reduce LLM call accuracy)
• Use modern LangChain tools that support Zod Schema (e.g. StructuredTool) for best results
• You can override the tool name and description via options to better fit the current Agent context
• The adapter automatically handles AbortSignal passing, but some older tools may not support it