Evaluating and iterating on AI apps with Lovable

Add Braintrust logging to [project name]'s Edge Function following this pattern:

1. Import the Braintrust SDK at the top of the Edge Function file.
2. Initialize the logger in the request handler using env var BRAINTRUST_API_KEY, with projectName set to your Braintrust project. Use asyncFlush: false to send logs immediately.
3. Create a root span named `request` and child spans for each major step (e.g., `ai_call`, `processing`).
   - Wrap main logic with `braintrust.traced(..., { name: "request" })`.
   - Create child spans with `rootSpan.startSpan("step_name")` and always `await span.end()` in `finally`.
   - Log input and output at each span for detailed tracing.
   - Provide a safe fallback path if the logger is unavailable.
4. Log inputs with clear fields (e.g., userPrompt, systemPrompt in metadata, not nested in messages).
5. Log outputs with both preview and full response.
6. If you later handle images, log full base64 data URLs: `data:image/[type];base64,[data]`.
7. Handle all errors and end spans in finally blocks.
8. Use or adapt this template:
import { serve } from "https://deno.land/[email protected]/http/server.ts";

// Import Braintrust SDK
let braintrust: any = null;
try {
  braintrust = await import("https://esm.sh/[email protected]");
} catch (e) {
  // Braintrust not available, continue without logging
}

const corsHeaders = {
  "Access-Control-Allow-Origin": "*",
  "Access-Control-Allow-Headers": "authorization, x-client-info, apikey, content-type",
};

serve(async (req) => {
  if (req.method === "OPTIONS") {
    return new Response(null, { headers: corsHeaders });
  }

  try {
    // Initialize logger
    const BRAINTRUST_API_KEY = Deno.env.get("BRAINTRUST_API_KEY");
    const logger = braintrust && BRAINTRUST_API_KEY
      ? braintrust.initLogger({
        projectName: "YOUR_PROJECT_NAME", // Replace with your project name
        apiKey: BRAINTRUST_API_KEY,
        asyncFlush: false,
      })
      : null;

    // Process request with or without Braintrust
    if (logger) {
      return await braintrust.traced(async (rootSpan: any) => {
        try {
          const body = await req.json();

          // Log input at root span
          await rootSpan?.log({ input: body });

          // ============================================
          // CHILD SPAN EXAMPLE
          // ============================================
          const childSpan = rootSpan.startSpan("example_step");
          let stepResult;
          try {
            // ← Add your logic here
            // Example: stepResult = await yourFunction(body);
            stepResult = body; // Placeholder - replace with your actual logic

            await childSpan?.log({
              input: body,
              output: stepResult
            });
          } finally {
            await childSpan?.end();
          }

          // Add more child spans as needed...

          // Log output at root span
          const finalResult = stepResult; // ← Replace with your actual result
          await rootSpan?.log({ output: finalResult });
          await rootSpan?.end();

          return new Response(JSON.stringify(finalResult), {
            headers: { ...corsHeaders, "Content-Type": "application/json" },
          });
        } catch (error: any) {
          await rootSpan?.log({ error: error?.message });
          await rootSpan?.end();
          throw error;
        }
      }, { name: "request" });
    } else {
      // Fallback without Braintrust
      const body = await req.json();
      // ← Add your logic here (same as above, just without spans)
      // Example: const result = await yourFunction(body);
      const result = body; // Placeholder - replace with your actual logic
      return new Response(JSON.stringify(result), {
        headers: { ...corsHeaders, "Content-Type": "application/json" },
      });
    }
  } catch (error: any) {
    return new Response(JSON.stringify({ error: error?.message }), {
      status: 500,
      headers: corsHeaders,
    });
  }
});

import { Eval } from "braintrust";
import { z } from "zod";

export default Eval("My Function Remote Eval", {
  task: async (input, { parameters }) => {
    const functionUrl = parameters?.functionUrl || input?.functionUrl;
    const systemPrompt =
      parameters?.systemPrompt || input?.systemPrompt || "You are a helpful assistant.";
    const userPrompt = parameters?.userPrompt || input?.userPrompt;

    if (!functionUrl) throw new Error("Missing functionUrl");

    const resp = await fetch(functionUrl, {
      method: "POST",
      headers: { "Content-Type": "application/json" },
      body: JSON.stringify(input || {}),
    });

    if (!resp.ok) throw new Error(`Function error ${resp.status}: ${await resp.text()}`);

    return await resp.json();
  },

  scores: [],

  parameters: {
    functionUrl: z.string().describe("Supabase Edge Function URL").default("https://your-project.supabase.co/functions/v1/your-function"),
  },
});

npx braintrust eval my-function-eval.js --dev --dev-host 0.0.0.0 --dev-port 8400
npx cloudflared tunnel --url http://localhost:8400