Chapter 1: Add weather tool (first tool)

- Add lib/ai/tools/get-weather.ts with geocoding support
- Update route.ts to import and use weather tool
- Add stepCountIs for multi-step tool conversations
- Add experimental_activeTools for reasoning model compatibility
- Update types.ts to use InferUITool for weather tool

Author: NiallJoeMaher

app/(chat)/api/chat/route.ts

@@ -4,8 +4,10 @@ import {
   createUIMessageStream,
   JsonToSseTransformStream,
   smoothStream,
+  stepCountIs,
   streamText,
 } from "ai";
+import { getWeather } from "@/lib/ai/tools/get-weather";
 import { unstable_cache as cache } from "next/cache";
 import type { ModelCatalog } from "tokenlens/core";
 
@@ -175,7 +177,15 @@ export async function POST(request: Request) {
           model: myProvider.languageModel(selectedChatModel),
           system: systemPrompt({ selectedChatModel, requestHints }),
           messages: convertToModelMessages(uiMessages),
+          stopWhen: stepCountIs(5),
+          experimental_activeTools:
+            selectedChatModel === "chat-model-reasoning"
+              ? []
+              : ["getWeather"],
           experimental_transform: smoothStream({ chunking: "word" }),
+          tools: {
+            getWeather,
+          },
           experimental_telemetry: {
             isEnabled: isProductionEnvironment,
             functionId: "stream-text",

lib/ai/tools/get-weather.ts

@@ -0,0 +1,78 @@
+import { tool } from "ai";
+import { z } from "zod";
+
+async function geocodeCity(
+  city: string
+): Promise<{ latitude: number; longitude: number } | null> {
+  try {
+    const response = await fetch(
+      `https://geocoding-api.open-meteo.com/v1/search?name=${encodeURIComponent(city)}&count=1&language=en&format=json`
+    );
+
+    if (!response.ok) {
+      return null;
+    }
+
+    const data = await response.json();
+
+    if (!data.results || data.results.length === 0) {
+      return null;
+    }
+
+    const result = data.results[0];
+    return {
+      latitude: result.latitude,
+      longitude: result.longitude,
+    };
+  } catch {
+    return null;
+  }
+}
+
+export const getWeather = tool({
+  description:
+    "Get the current weather at a location. You can provide either coordinates or a city name.",
+  inputSchema: z.object({
+    latitude: z.number().optional(),
+    longitude: z.number().optional(),
+    city: z
+      .string()
+      .describe("City name (e.g., 'San Francisco', 'New York', 'London')")
+      .optional(),
+  }),
+  execute: async (input) => {
+    let latitude: number;
+    let longitude: number;
+
+    if (input.city) {
+      const coords = await geocodeCity(input.city);
+      if (!coords) {
+        return {
+          error: `Could not find coordinates for "${input.city}". Please check the city name.`,
+        };
+      }
+      latitude = coords.latitude;
+      longitude = coords.longitude;
+    } else if (input.latitude !== undefined && input.longitude !== undefined) {
+      latitude = input.latitude;
+      longitude = input.longitude;
+    } else {
+      return {
+        error:
+          "Please provide either a city name or both latitude and longitude coordinates.",
+      };
+    }
+
+    const response = await fetch(
+      `https://api.open-meteo.com/v1/forecast?latitude=${latitude}&longitude=${longitude}&current=temperature_2m&hourly=temperature_2m&daily=sunrise,sunset&timezone=auto`
+    );
+
+    const weatherData = await response.json();
+
+    if ("city" in input) {
+      weatherData.cityName = input.city;
+    }
+
+    return weatherData;
+  },
+});

lib/types.ts

@@ -1,7 +1,7 @@
-import type { UIMessage } from "ai";
+import type { InferUITool, UIMessage } from "ai";
 import { z } from "zod";
 import type { ArtifactKind } from "@/components/artifact";
-import type { WeatherAtLocation } from "@/components/weather";
+import type { getWeather } from "./ai/tools/get-weather";
 import type { Suggestion } from "./db/types";
 import type { AppUsage } from "./usage";
 
@@ -13,8 +13,10 @@ export const messageMetadataSchema = z.object({
 
 export type MessageMetadata = z.infer<typeof messageMetadataSchema>;
 
-// Tool type definitions for UI rendering
-// These are placeholders in Chapter 0 - tools not registered in the API
+// Tool types - inferred from actual tool definitions
+type weatherTool = InferUITool<typeof getWeather>;
+
+// Placeholder types for tools not yet implemented
 // UITools expects { input, output } shape for each tool
 type DocumentResult = {
   id: string;
@@ -23,10 +25,7 @@ type DocumentResult = {
 };
 
 export type ChatTools = {
-  getWeather: {
-    input: { latitude: number; longitude: number };
-    output: WeatherAtLocation;
-  };
+  getWeather: weatherTool;
   createDocument: {
     input: { title: string; kind: ArtifactKind };
     output: DocumentResult | { error: string };