I Built 6 Free Developer Tools for AI APIs, Cron, Docker, and Self-Hosting

I keep running into the same friction points: "How much will this prompt cost on GPT-4o vs Claude?", "What's the cron syntax for every Monday at 9am?", "Is there an open-source alternative to Notion I can self-host?"

I got tired of Googling each time, so I built a set of free tools that solve these problems. No login, no API keys, no tracking — everything runs in your browser.

Here's what each one does.

1. AI Prompt Cost Calculator

Paste any prompt and instantly see the cost across 10 AI models: GPT-4o, GPT-4o Mini, o3, o4-mini, Claude Sonnet 4, Claude Haiku 4, Gemini 2.5 Pro, Gemini 2.5 Flash, Llama 4 Maverick (via Groq), and DeepSeek R1.

It uses

2. Cron Expression Generator

161 cron expressions covering every common pattern. Each one comes with a plain-English explanation and the next 5 run times.

Some examples:

• 
  */5 * * * * — Every 5 minutes


• 
  0 * * * * — Every hour


• 
  0 9 * * 1 — Every Monday at 9:00 AM


• 
  0 0 1 * * — First day of every month

There's also a builder mode where you select the schedule and it generates the expression for you.

Try it:

4. Docker Deploy Generator

One-click Docker Compose configs for 30 self-hosted applications. Copy, edit the environment variables, and run docker compose up -d.

Each config includes:

• The official Docker image


• Persistent volume mounts


• Common environment variables with sensible defaults


• Port mappings

Try it:

6. AI Agent Safety Checklist

18 items across 8 categories for anyone building production AI agents:

• Input validation


• Tool & API security


• Prompt injection defense


• Data privacy


• Access control


• Monitoring & logging


• Error handling


• Supply chain security

Each item has a severity level (critical/warning/info) and an explanation of why it matters. Check items off as you go — your progress is saved in localStorage.

Try it: with 240 pages total (mostly from the cron generator and its long-tail expressions).

What's Next

I'm working on:

• Batch prompt cost calculation (upload a CSV)


• More voice AI providers


• i18n for the cron generator (Chinese and Japanese)

Feedback and suggestions welcome. What developer tools are you always Googling for?