What is App Stack Builder?

App Stack Builder is a free AI-powered tool that helps founders and developers choose the right tech stack for their projects based on budget, app type, team size, and skill level.

What is the best tech stack for SaaS in 2026?

The best tech stack for SaaS in 2026 typically includes Next.js 16 for frontend, Supabase for database and auth, Vercel for hosting, Stripe for payments, and PostHog for analytics. App Stack Builder can generate a personalized recommendation based on your specific budget and requirements.

Is App Stack Builder free to use?

Yes, App Stack Builder is completely free to use. You can generate unlimited tech stack recommendations without any cost.

What types of apps can I build with the recommended stacks?

App Stack Builder supports various app types including SaaS applications, web apps, mobile apps, e-commerce stores, internal tools, and AI/ML products.

How much does a SaaS tech stack cost per month?

A modern SaaS tech stack can cost anywhere from $0-50/month for bootstrapped startups using free tiers, $100-300/month for growth-stage startups, to $500+/month for enterprise-ready infrastructure. App Stack Builder helps you find the best tools within your specific budget.

What is the best tech stack for solo founders?

For solo founders, we recommend Next.js + Vercel (free), Supabase (free tier), Supabase Auth (free), Stripe (pay as you go), and Plausible or PostHog for analytics. This stack can run your entire SaaS for under $50/month.

Can I export my tech stack recommendations?

Yes, you can export your tech stack recommendations as a PDF document or copy them to your clipboard. You can also share a link to your stack with others.

AI Evals & Agent Testing

Best AI Evals & Agent Testing Tools in 2026

Changing a prompt or swapping a model can quietly break answers that worked yesterday. Eval tools catch that before users do: they run test cases against your LLM app or agent and score the results. Here are the leading options in 2026, from free open-source frameworks you run in CI to a platform that simulates callers for voice agents.

AI Evals & Agent Testing Tools Compared

Tool	Pricing	Free tier
DeepEval	Free · paid from $200/mo
Promptfoo	Free · paid plans by quote
Ragas	Free
Coval	From $100/mo	—

The Best AI Evals & Agent Testing Tools, Ranked

1. DeepEval

Free tier· Free · paid from $200/mo

Open-source, pytest-style framework for unit testing LLM apps and agents, with 50+ metrics. Confident AI is its hosted platform.

Feels like unit testing, runs in pytest
Agent metrics like tool correctness
Free and open source

DeepEval & alternatives

2. Promptfoo

Free tier· Free · paid plans by quote

Open-source CLI for testing prompts, agents and RAG apps, with built-in red teaming for jailbreaks, prompt injection and data leaks.

Free and open source (MIT)
Best-known red-teaming suite for LLM apps
Config-file tests that run in CI

Promptfoo & alternatives

3. Ragas

Free tier· Free

Open-source library for evaluating RAG pipelines: faithfulness, context precision and recall, plus synthetic test set generation.

The reference metrics for RAG quality
Generates test sets from your documents
Free and open source

Ragas & alternatives

4. Coval

· From $100/mo

Simulation and monitoring for voice AI agents: test against simulated callers and personas before launch, then score live calls.

Built for voice agents, with realistic simulated callers
Testing and production monitoring in one
Published prices and unlimited seats

Coval & alternatives

How to choose a ai evals & agent testing tool

Start with what you are testing. A prompt or agent needs general evals, a RAG pipeline needs retrieval metrics, and a voice agent needs simulated conversations.
Choose Promptfoo for config-file tests across models and the best-known red-teaming suite. It is free and open source.
Choose DeepEval if you want LLM tests that look like unit tests and run in pytest, with agent metrics such as tool correctness.
Choose Ragas to measure retrieval quality and faithfulness in a RAG pipeline, and to generate test questions from your own documents.
Choose Coval to test a voice agent against simulated callers before launch and keep scoring live calls after.
For a hosted dashboard with traces, datasets and production evals, see LLM Observability & Evals.

Frequently Asked Questions

What are the best ai evals & agent testing tools for startups in 2026?⌄

The best ai evals & agent testing tools for startups in 2026 include DeepEval, Promptfoo, Ragas, Coval. Compare them by pricing, free tiers, and features in the list above.

What is the best free ai evals & agent testing tool?⌄

Free ai evals & agent testing options include DeepEval, Promptfoo, Ragas — all offer a free tier suitable for bootstrapped startups and MVPs.

How do I choose a ai evals & agent testing tool?⌄

Start with your budget and team size, prefer tools with a free tier to validate, and make sure your pick integrates with the rest of your stack. App Stack Builder can recommend a complete, budget-aware stack in about 60 seconds.

Need the whole stack, not just ai evals & agent testing?

Get a free, AI-powered tech stack — matched to your budget, app type, and team size in 60 seconds.

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