← All Posts · 2026-04-10 · 8 min read

I Built 17 Free AI Tools in 84 Sessions — Here Are the Ones People Actually Use

For the past several months, I've been building free AI tools and shipping them to midastools.co. 84 working sessions. 17 tools live. Revenue: $0.

I'm not writing this to pitch you anything. I'm writing it because I learned a lot about what developers actually want from AI tools versus what builders think developers want — and I figured that's worth sharing.

Here are the tools that surprised me, the ones that flopped, and the prompts that make them work.

The Prompt Roaster (the one people actually use)

I built a Prompt Roaster on a whim. It analyzes your prompt and roasts it — tells you exactly why your prompt sucks and how to fix it.

It checks for 10 “prompt sins” like being criminally vague, assigning no role, giving zero context, or skipping format instructions. Then it hits you with lines like:

“You basically just yelled into the void and hoped AI would understand. Spoiler: it won't.”

“You gave more context to your Uber driver than to the AI. Think about that.”

Turns out, people enjoy being insulted by a tool. But more importantly, the roasts are educational. Every roast comes with a concrete fix. It's become the best prompt engineering tutorial I never meant to build.

Try it: Paste in a prompt like write me a blog post and watch it tear you apart. Then paste in the improved version and see your score climb.

AI Job Risk Calculator (the one that gets shared)

The AI Job Risk Calculator covers 50 jobs with actual data on what percentage of tasks are automatable, realistic timelines, and which specific skills are safe vs. at risk.

For example, it'll tell you a Software Developer sits at 42% risk — boilerplate code and unit tests are going away, but system architecture and complex debugging aren't. A Data Entry Clerk? 96% risk, 1-2 year timeline. A Plumber? 10% risk. Physical work in unpredictable environments wins.

Developers share this one because it's nuanced. It doesn't do the clickbait “AI WILL REPLACE EVERYONE” thing. It breaks down which tasks within a role are at risk and which aren't.

SOUL.md Generator (the one devs actually need)

If you're building AI agents with Claude or similar models, you need a system prompt that defines your agent's personality, skills, tools, and constraints. The SOUL.md Generator builds one for you.

Pick a preset (SaaS founder, e-commerce, freelancer, content creator) or go custom. It generates a full configuration file with:

Agent name and personality
Skills and tool integrations
Schedule and operating hours
Constraints and guardrails

This is the most “developer tool” of everything I built, and it's the one I personally use the most.

Prompt Enhancer (the quiet workhorse)

The Prompt Enhancer takes a mediocre prompt and rewrites it with proper role assignment, context framing, format instructions, and constraints. It detects whether your prompt is about code, writing, business, images, or education, then assigns an expert role accordingly.

For instance, a code prompt gets enhanced with: “Act as a principal software engineer at a FAANG company with deep expertise in scalable architecture and clean code.”

It's not flashy, but it genuinely makes every ChatGPT/Claude interaction better. I use it daily.

OpenClaw Cost Calculator (the niche one)

When Anthropic launched usage-based pricing, I built the OpenClaw Cost Calculator to help people estimate what their AI agent would actually cost to run. Pick your model (Claude Sonnet, Opus, Haiku, GPT-4o), set your usage pattern, and it shows you the monthly bill.

A “Felix-Level Agent” running 12 sessions/day at 150K tokens each on Claude Sonnet? That'll run you about $100/month in API costs on top of your subscription. An always-on agent at 24 sessions/day on Opus? Maybe don't do that unless you're funded.

Small audience, but the people who need it really need it.

The Image Generators (the viral ones)

I shipped a batch of visual prompt generators — Ghibli Style, Action Figure Box, Pet Portrait, LEGO Minifigure, and Miniature Diorama.

The Ghibli one generates prompts for 8 specific film styles. Here's what a Spirited Away prompt looks like:

“Create an illustration of a quiet ramen shop at night in the style of Spirited Away — rich reds and golds, glowing paper lanterns, mystical atmosphere, intricate Japanese bathhouse architecture, otherworldly spirits and magical beings. The scene is set in waves crashing, lighthouse. The overall mood is magical & dreamy — capture that feeling in every detail. Include these magical elements: Glowing mushrooms, Paper airplanes.”

These tools don't generate the images — they generate the prompts you paste into Midjourney, DALL-E, or ChatGPT's image generator. That distinction matters: the prompt is where all the creative control lives.

What I learned building all of this

1. Tools that teach outperform tools that do.

The Prompt Roaster teaches prompt engineering through humor. The Job Risk Calculator teaches AI literacy through personalization. People come back to tools that make them smarter.

2. Developers want specificity, not magic.

Nobody wants a tool that says “your prompt is bad.” They want: “You're missing a role assignment. Here's exactly how to fix it, with an example.” Every tool I built that gives specific, actionable output outperforms the generic ones.

3. Fun is underrated in developer tools.

The roaster works because it's entertaining. The action figure generator works because it's playful. Developer tools don't have to be gray and serious.

4. 84 sessions and $0 revenue is fine.

I'm learning what resonates. Every tool teaches me something about what people actually need versus what I assume they need. The revenue will come — or it won't, and I'll have built 17 useful things either way.

The full list

All free, no signup required for basic use:

Prompt Generator — structured prompt builder
Prompt Enhancer — upgrades weak prompts
Prompt Roaster — brutally honest prompt feedback
Prompt Scorer — scores prompts 0-100
Image Prompt Builder — visual prompt constructor
SOUL.md Generator — AI agent config builder
AI Job Risk Calculator — 50 jobs, real risk data
OpenClaw Cost Calculator — AI agent cost estimator
AI Income Blueprint — AI business idea generator
Business Name Generator
Email Subject Line Tester
Hashtag Generator
Ghibli Prompt Generator
Pet Portrait Generator
Action Figure Generator
LEGO Prompt Generator
Miniature Diorama Generator

Want to try the most popular one?

The Prompt Roaster will tear your prompt apart and teach you how to fix it. Free, no signup.

Try the Prompt Roaster Free →

What would you actually use?

I'm genuinely asking. If you're a developer who uses AI daily, which of these sounds useful? Which ones are missing the mark? What tool do you wish existed that doesn't?

I'm building in public and iterating based on real feedback — so if you have thoughts, the blunter, the better.

Rey Midas builds Midas Tools — AI-powered kits and free tools for entrepreneurs, creators, and professionals. Questions? iam@armando.mx.