Tools & Chat

Effect AI enables you to build sophisticated AI agents by combining tool calling with stateful chat sessions. This page covers defining tools, implementing handlers, and managing conversations.

Tools

Tools allow AI models to perform actions like calling APIs, querying databases, or executing code within your application context.

Defining Tools

Create a tool using Tool.make with a name, description, parameters schema, and success schema:

import { Schema } from "effect"
import { Tool } from "effect/unstable/ai"

const GetWeather = Tool.make("GetWeather", {
  description: "Get current weather for a location",
  parameters: Schema.Struct({
    location: Schema.String.pipe(
      Schema.annotations({ description: "City name, e.g. 'San Francisco'" })
    ),
    units: Schema.Literals("celsius", "fahrenheit").pipe(
      Schema.withDecodingDefault(() => "celsius" as const)
    )
  }),
  success: Schema.Struct({
    temperature: Schema.Number,
    condition: Schema.String,
    humidity: Schema.Number
  })
})

Tool Options

Description: Helps the model understand when to use the tool

const SearchDatabase = Tool.make("SearchDatabase", {
  description: "Search the product database by keyword. Use this when the user asks about products, inventory, or pricing.",
  parameters: Schema.Struct({ query: Schema.String }),
  success: Schema.Array(ProductSchema)
})

Failure Schemas: Define expected error types

const DeleteUser = Tool.make("DeleteUser", {
  description: "Delete a user account",
  parameters: Schema.Struct({ userId: Schema.String }),
  success: Schema.Struct({ deleted: Schema.Boolean }),
  failure: Schema.Struct({
    error: Schema.Literals("not_found", "permission_denied")
  }),
  failureMode: "return" // Return failures instead of throwing
})

Needs Approval: Require user approval before execution

const SendEmail = Tool.make("SendEmail", {
  description: "Send an email",
  parameters: Schema.Struct({
    to: Schema.String,
    subject: Schema.String,
    body: Schema.String
  }),
  success: Schema.Struct({ sent: Schema.Boolean }),
  needsApproval: true // Always require approval
})

// Or conditional approval
const TransferMoney = Tool.make("TransferMoney", {
  description: "Transfer money between accounts",
  parameters: Schema.Struct({
    amount: Schema.Number,
    from: Schema.String,
    to: Schema.String
  }),
  success: Schema.Struct({ transactionId: Schema.String }),
  needsApproval: ({ amount }) => amount > 1000 // Only large transfers
})

Toolkits

Group related tools into a toolkit:

import { Effect } from "effect"
import { Tool, Toolkit } from "effect/unstable/ai"

const GetCurrentTime = Tool.make("GetCurrentTime", {
  description: "Get the current time",
  success: Schema.String
})

const GetWeather = Tool.make("GetWeather", {
  description: "Get current weather",
  parameters: Schema.Struct({ location: Schema.String }),
  success: Schema.Struct({
    temperature: Schema.Number,
    condition: Schema.String
  })
})

const SearchWeb = Tool.make("SearchWeb", {
  description: "Search the web",
  parameters: Schema.Struct({ query: Schema.String }),
  success: Schema.Array(Schema.Struct({
    title: Schema.String,
    url: Schema.String,
    snippet: Schema.String
  }))
})

// Create a toolkit
const AssistantToolkit = Toolkit.make(
  GetCurrentTime,
  GetWeather,
  SearchWeb
)

Implementing Handlers

Convert a toolkit to a Layer with handler implementations:

import { DateTime, Effect, Layer } from "effect"

const AssistantToolkitLayer = AssistantToolkit.toLayer(
  Effect.gen(function*() {
    // Access any services you need
    const weatherService = yield* WeatherService
    const searchService = yield* SearchService
    
    return AssistantToolkit.of({
      GetCurrentTime: Effect.fn("AssistantToolkit.GetCurrentTime")(
        function*() {
          const now = yield* DateTime.now
          return DateTime.formatIso(now)
        }
      ),
      
      GetWeather: Effect.fn("AssistantToolkit.GetWeather")(
        function*({ location }) {
          return yield* weatherService.getCurrentWeather(location)
        }
      ),
      
      SearchWeb: Effect.fn("AssistantToolkit.SearchWeb")(
        function*({ query }) {
          const results = yield* searchService.search(query)
          return results.slice(0, 5)
        }
      )
    })
  })
).pipe(
  Layer.provide(WeatherServiceLive),
  Layer.provide(SearchServiceLive)
)

Using Tools with LanguageModel

Pass a toolkit to enable tool calling:

import { Effect } from "effect"
import { LanguageModel } from "effect/unstable/ai"

const program = Effect.gen(function*() {
  const toolkit = yield* AssistantToolkit
  
  const response = yield* LanguageModel.generateText({
    prompt: "What's the weather in San Francisco and what time is it?",
    toolkit
  })
  
  console.log("Response:", response.text)
  console.log("Tool calls made:", response.toolCalls.length)
  
  // Inspect tool calls
  for (const call of response.toolCalls) {
    console.log(`Called ${call.name} with:`, call.params)
  }
  
  // Inspect tool results
  for (const result of response.toolResults) {
    console.log(`Result from ${result.name}:`, result.result)
    console.log(`Failed: ${result.isFailure}`)
  }
})

const runnable = program.pipe(
  Effect.provide(modelLayer),
  Effect.provide(AssistantToolkitLayer)
)

Tool Choice Control

Control how the model uses tools:

// Auto (default): Model decides whether to call tools
const response1 = yield* LanguageModel.generateText({
  prompt: "Hello!",
  toolkit,
  toolChoice: "auto"
})

// None: Disable tool calling
const response2 = yield* LanguageModel.generateText({
  prompt: "Hello!",
  toolkit,
  toolChoice: "none"
})

// Required: Force the model to call at least one tool
const response3 = yield* LanguageModel.generateText({
  prompt: "What's the weather?",
  toolkit,
  toolChoice: "required"
})

// Specific tool: Force a particular tool
const response4 = yield* LanguageModel.generateText({
  prompt: "Weather please",
  toolkit,
  toolChoice: { tool: "GetWeather" }
})

// Subset of tools: Restrict to specific tools
const response5 = yield* LanguageModel.generateText({
  prompt: "Help me",
  toolkit,
  toolChoice: {
    mode: "required",
    oneOf: ["GetWeather", "GetCurrentTime"]
  }
})

Provider-Defined Tools

Some providers offer built-in tools like web search or code execution:

import { OpenAiTool } from "@effect/ai-openai"
import { AnthropicTool } from "@effect/ai-anthropic"

// OpenAI tools
const webSearch = OpenAiTool.WebSearch({
  search_context_size: "medium"
})

const codeInterpreter = OpenAiTool.CodeInterpreter()

const fileSearch = OpenAiTool.FileSearch({
  vector_store_ids: ["vs_abc123"]
})

// Anthropic tools
const computerUse = AnthropicTool.ComputerUse({
  display_width_px: 1920,
  display_height_px: 1080
})

const bash = AnthropicTool.Bash()

// Combine with user-defined tools
const mixedToolkit = Toolkit.make(
  GetWeather,
  GetCurrentTime,
  webSearch,
  codeInterpreter
)

Provider-defined tools are executed server-side and don’t require handlers in your application.

Chat

The Chat module provides stateful conversation sessions with automatic history management.

Creating a Chat Session

Create an empty chat or initialize with a prompt:

import { Effect } from "effect"
import { Chat, Prompt } from "effect/unstable/ai"

// Empty chat
const chat1 = yield* Chat.empty

// With initial prompt
const chat2 = yield* Chat.fromPrompt("Hello!")

// With system message
const chat3 = yield* Chat.fromPrompt([
  {
    role: "system",
    content: "You are a helpful coding assistant."
  }
])

// Using Prompt utilities
const systemPrompt = Prompt.empty.pipe(
  Prompt.setSystem("You are a helpful assistant.")
)
const chat4 = yield* Chat.fromPrompt(systemPrompt)

Multi-Turn Conversations

The chat automatically maintains history:

import { Effect } from "effect"
import { Chat } from "effect/unstable/ai"

const program = Effect.gen(function*() {
  const chat = yield* Chat.fromPrompt([
    {
      role: "system",
      content: "You are a helpful assistant."
    }
  ])
  
  // First turn
  const response1 = yield* chat.generateText({
    prompt: "What's the capital of France?"
  })
  console.log("Assistant:", response1.text)
  
  // Second turn - chat remembers previous context
  const response2 = yield* chat.generateText({
    prompt: "What's its population?"
  })
  console.log("Assistant:", response2.text)
  
  // Third turn
  const response3 = yield* chat.generateText({
    prompt: "What are some famous landmarks there?"
  })
  console.log("Assistant:", response3.text)
})

const runnable = program.pipe(
  Effect.provide(modelLayer)
)

Streaming Chat

Stream responses while maintaining history:

import { Effect, Stream } from "effect"
import { Chat } from "effect/unstable/ai"

const program = Effect.gen(function*() {
  const chat = yield* Chat.empty
  
  const stream = chat.streamText({
    prompt: "Write a short story about space"
  })
  
  yield* Stream.runForEach(stream, (part) => {
    if (part.type === "text-delta") {
      return Effect.sync(() => process.stdout.write(part.delta))
    }
    return Effect.void
  })
  
  // History is updated after streaming completes
  const response2 = yield* chat.generateText({
    prompt: "What was the main character's name?"
  })
  console.log("\nAssistant:", response2.text)
})

Structured Output with Chat

Generate validated objects while maintaining history:

import { Schema } from "effect"
import { Chat } from "effect/unstable/ai"

const ContactSchema = Schema.Struct({
  name: Schema.String,
  email: Schema.String,
  phone: Schema.optional(Schema.String)
})

const program = Effect.gen(function*() {
  const chat = yield* Chat.empty
  
  const response = yield* chat.generateObject({
    prompt: "Extract contact: John Doe, [email protected]",
    schema: ContactSchema
  })
  
  console.log("Contact:", response.value)
  
  // Continue conversation
  const response2 = yield* chat.generateText({
    prompt: "Format that as a business card"
  })
  console.log("Card:", response2.text)
})

Building Agentic Loops

Create AI agents that use tools iteratively:

import { Effect } from "effect"
import { Chat, Tool, Toolkit } from "effect/unstable/ai"

const tools = Toolkit.make(
  Tool.make("SearchDatabase", {
    description: "Search the database",
    parameters: Schema.Struct({ query: Schema.String }),
    success: Schema.Array(Schema.Unknown)
  }),
  Tool.make("AnalyzeData", {
    description: "Analyze data",
    parameters: Schema.Struct({ data: Schema.Unknown }),
    success: Schema.String
  })
)

const agent = Effect.gen(function*() {
  const toolkit = yield* tools
  
  // Initialize chat with system prompt
  const chat = yield* Chat.fromPrompt([
    {
      role: "system",
      content: "You are an AI agent that helps analyze data. Use tools to gather and analyze information."
    },
    {
      role: "user",
      content: "Find and analyze recent sales data"
    }
  ])
  
  // Run agent loop until no more tool calls
  let maxIterations = 10
  while (maxIterations-- > 0) {
    const response = yield* chat.generateText({
      prompt: [], // Empty prompt - uses chat history
      toolkit
    })
    
    if (response.toolCalls.length === 0) {
      // Agent returned final answer
      return response.text
    }
    
    // Tool calls were executed and added to history automatically
    // Continue the loop
  }
  
  return "Agent exceeded max iterations"
})

const runnable = agent.pipe(
  Effect.provide(modelLayer),
  Effect.provide(toolsLayer)
)

Persisting Chat History

Export and restore chat sessions:

import { Effect } from "effect"
import { Chat } from "effect/unstable/ai"

// Export to JSON
const saveChat = Effect.gen(function*() {
  const chat = yield* Chat.empty
  
  yield* chat.generateText({ prompt: "Hello!" })
  yield* chat.generateText({ prompt: "How are you?" })
  
  // Export as JSON string
  const json = yield* chat.exportJson
  
  // Save to storage
  yield* Effect.sync(() => localStorage.setItem("chat-history", json))
  
  return json
})

// Restore from JSON
const loadChat = Effect.gen(function*() {
  const json = yield* Effect.sync(() => localStorage.getItem("chat-history"))
  
  if (!json) {
    return yield* Chat.empty
  }
  
  // Restore chat with full history
  const chat = yield* Chat.fromJson(json)
  
  // Continue conversation
  const response = yield* chat.generateText({
    prompt: "Let's continue our discussion"
  })
  
  return chat
})

Inspecting History

Access the conversation history directly:

import { Effect, Ref } from "effect"
import { Chat } from "effect/unstable/ai"

const program = Effect.gen(function*() {
  const chat = yield* Chat.empty
  
  yield* chat.generateText({ prompt: "Hello!" })
  
  // Get current history
  const history = yield* Ref.get(chat.history)
  
  console.log("Messages:", history.content.length)
  
  for (const message of history.content) {
    console.log(`${message.role}:`, message.content)
  }
  
  // Manually modify history if needed
  yield* Ref.update(chat.history, (h) => {
    // Transform history
    return h
  })
})

Complete Example: Customer Support Agent

Here’s a complete example combining tools and chat:

import { Effect, Schema, Layer, Config } from "effect"
import { Chat, Tool, Toolkit } from "effect/unstable/ai"
import { OpenAiClient, OpenAiLanguageModel } from "@effect/ai-openai"
import { FetchHttpClient } from "effect/unstable/http"

const OpenAiClientLayer = OpenAiClient.layerConfig({
  apiKey: Config.redacted("OPENAI_API_KEY")
}).pipe(Layer.provide(FetchHttpClient.layer))

// Define tools
const tools = Toolkit.make(
  Tool.make("GetCustomerInfo", {
    description: "Get customer information by ID",
    parameters: Schema.Struct({ customerId: Schema.String }),
    success: Schema.Struct({
      name: Schema.String,
      email: Schema.String,
      tier: Schema.Literals("free", "pro", "enterprise")
    })
  }),
  Tool.make("GetOrderStatus", {
    description: "Get order status by order ID",
    parameters: Schema.Struct({ orderId: Schema.String }),
    success: Schema.Struct({
      status: Schema.Literals("pending", "shipped", "delivered"),
      estimatedDelivery: Schema.String
    })
  }),
  Tool.make("CreateTicket", {
    description: "Create a support ticket",
    parameters: Schema.Struct({
      customerId: Schema.String,
      issue: Schema.String,
      priority: Schema.Literals("low", "medium", "high")
    }),
    success: Schema.Struct({ ticketId: Schema.String })
  })
)

const toolsLayer = tools.toLayer(
  Effect.gen(function*() {
    return tools.of({
      GetCustomerInfo: ({ customerId }) =>
        Effect.succeed({
          name: "John Doe",
          email: "[email protected]",
          tier: "pro" as const
        }),
      GetOrderStatus: ({ orderId }) =>
        Effect.succeed({
          status: "shipped" as const,
          estimatedDelivery: "2024-03-15"
        }),
      CreateTicket: ({ customerId, issue, priority }) =>
        Effect.succeed({ ticketId: `TKT-${Date.now()}` })
    })
  })
)

const supportAgent = Effect.gen(function*() {
  const toolkit = yield* tools
  const modelLayer = yield* OpenAiLanguageModel.model("gpt-4")
  
  const chat = yield* Chat.fromPrompt([
    {
      role: "system",
      content:
        "You are a helpful customer support agent. Use tools to look up customer " +
        "information, check order status, and create support tickets when needed."
    }
  ])
  
  // Handle a customer inquiry
  const response1 = yield* chat.generateText({
    prompt: "Hi, I'm customer C123 and want to check my order O456",
    toolkit
  }).pipe(Effect.provide(modelLayer))
  
  console.log("Agent:", response1.text)
  
  // Continue conversation
  const response2 = yield* chat.generateText({
    prompt: "It's taking too long, can you help?",
    toolkit
  }).pipe(Effect.provide(modelLayer))
  
  console.log("Agent:", response2.text)
})

const runnable = supportAgent.pipe(
  Effect.provide(toolsLayer),
  Effect.provide(OpenAiClientLayer)
)

Effect.runPromise(runnable)

Get Started

Core Concepts

Guides

HTTP

Data & Persistence

AI & LLM

Advanced

Migration

Tools

Defining Tools

Tool Options

Toolkits

Implementing Handlers

Using Tools with LanguageModel

Tool Choice Control

Provider-Defined Tools

Chat

Creating a Chat Session

Multi-Turn Conversations

Streaming Chat

Structured Output with Chat

Building Agentic Loops

Persisting Chat History

Inspecting History

Complete Example: Customer Support Agent

Next Steps

Language Models

AI Overview

Build docs developers (and LLMs) love

Get Started

Core Concepts

Guides

HTTP

Data & Persistence

AI & LLM

Advanced

Migration

​Tools

​Defining Tools

​Tool Options

​Toolkits

​Implementing Handlers

​Using Tools with LanguageModel

​Tool Choice Control

​Provider-Defined Tools

​Chat

​Creating a Chat Session

​Multi-Turn Conversations

​Streaming Chat

​Structured Output with Chat

​Building Agentic Loops

​Persisting Chat History

​Inspecting History

​Complete Example: Customer Support Agent

​Next Steps

Language Models

AI Overview

Build docs developers (and LLMs) love

Tools

Defining Tools

Tool Options

Toolkits

Implementing Handlers

Using Tools with LanguageModel

Tool Choice Control

Provider-Defined Tools

Chat

Creating a Chat Session

Multi-Turn Conversations

Streaming Chat

Structured Output with Chat

Building Agentic Loops

Persisting Chat History

Inspecting History

Complete Example: Customer Support Agent

Next Steps