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 tiktoken for exact OpenAI token counts and estimates for other models (~4 chars/token for English, ~1.5 for Chinese). You can adjust monthly call volume and expected output tokens to see projected monthly costs.

Try it: AI Prompt Cost Calculator

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: Cron Expression Generator

3. Self-Hosted Alternatives

36 popular SaaS tools, each with open-source alternatives you can self-host. Some examples:

SaaS	Self-Hosted Alternative
Slack	Mattermost
Notion	Outline
Google Drive	Nextcloud
1Password	Vaultwarden
Trello	WeKan
Zoom	Jitsi Meet

Each alternative has a feature comparison and a link to its Docker deployment config (see tool #4).

Try it: Self-Hosted Alternatives

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: Docker Deploy Generator

5. Voice AI Pricing Calculator

Compare TTS (text-to-speech) and STT (speech-to-text) pricing across 6 providers: OpenAI, ElevenLabs, Deepgram, AssemblyAI, Google Cloud, and Azure.

Enter your expected monthly character volume and see costs for each provider side by side. There are also preset buttons for common volumes (100K, 1M, 5M, 10M characters/month).

This was born out of my own frustration trying to compare voice AI pricing — each provider uses different pricing units (per character, per 15 seconds, per minute) making direct comparison painful.

Try it: Voice AI Pricing Calculator

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: AI Agent Safety Checklist

Tech Stack

All 6 tools are static React apps built with Vite and Tailwind CSS. No backend, no database, no user accounts. Everything runs client-side.

The entire collection lives at prompt-cost-calculator-ten.vercel.app with 240 pages total (mostly from the cron generator and its long-tail expressions).