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Jack

Posted on • Originally published at anethoth.com

11 Free APIs Every Developer Should Bookmark (No Signup Required)

#webdev #api #tutorial #productivity

Every developer needs a handful of utility APIs — the kind you reach for when building prototypes, debugging integrations, or automating workflows. Here are 11 free ones I built. No signup, no API key, no rate limit surprises.

1. HTML to PDF Converter

Convert any HTML to a clean PDF. Supports A4, Letter, Legal page sizes.

curl -X POST https://documint.anethoth.com/api/v1/html-to-pdf   -H "Content-Type: application/json"   -d '{"html": "<h1>Hello World</h1><p>This becomes a PDF.</p>"}'   --output result.pdf
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2. Markdown to PDF

Write Markdown, get a styled PDF with proper headings, code blocks, and lists.

curl -X POST https://documint.anethoth.com/api/v1/markdown-to-pdf   -H "Content-Type: application/json"   -d '{"markdown": "# Report\n\n## Summary\n\nThis is a **styled** document."}'   --output report.pdf
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3. Cron Expression Parser

Describe any cron expression in plain English.

curl "https://cronping.anethoth.com/api/v1/cron/describe?expr=*/5+*+*+*+*"
# {"description": "Every 5 minutes", ...}
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4. Cron Next Run Calculator

Get the next N scheduled run times for any cron expression.

curl "https://cronping.anethoth.com/api/v1/cron/next?expr=0+9+*+*+1&count=5"
# Returns next 5 Monday 9 AM times
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5. Cron Expression Validator

Validate cron expressions before deploying them.

curl "https://cronping.anethoth.com/api/v1/cron/validate?expr=0+25+*+*+*"
# {"valid": false, "error": "Minute value 25 out of range..."}
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6. HTTP Echo

Send any HTTP request, get it mirrored back as JSON. Perfect for debugging.

curl -X POST https://webhookvault.anethoth.com/api/v1/echo   -H "Authorization: Bearer test123"   -d '{"test": true}'
# Returns: method, headers, body, IP, timestamp
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7. HTTP Headers Inspector

See exactly what headers your client is sending.

curl https://webhookvault.anethoth.com/api/v1/headers
# Returns all headers with auth type detection
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8. Feature Flag Evaluation Playground

Test feature flag targeting rules without creating an account.

curl -X POST https://flagbit.anethoth.com/api/v1/evaluate-playground   -H "Content-Type: application/json"   -d '{"rules": [{"attribute": "country", "operator": "eq", "value": "US", "result": true}], "context": {"country": "US"}}'
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9. Rollout Simulator

Simulate percentage rollouts across N users with consistent hashing.

curl "https://flagbit.anethoth.com/api/v1/rollout/simulate?flag=new-checkout&percentage=25&users=100"
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10. Rollout Bucket Lookup

Check which rollout bucket a specific user falls into.

curl "https://flagbit.anethoth.com/api/v1/rollout/bucket?flag=dark-mode&user_id=user_42"
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11. Free Invoice Generator

Generate professional PDF invoices from JSON. 3 templates (classic, modern, minimal).

curl -X POST https://documint.anethoth.com/api/v1/demo-invoice   -H "Content-Type: application/json"   -d '{"company_name": "Acme", "items": [{"description": "Consulting", "quantity": 10, "unit_price": 150}]}'   --output invoice.pdf
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All endpoints support CORS

Every API listed above allows cross-origin requests, so you can call them from browser JavaScript:

const resp = await fetch("https://cronping.anethoth.com/api/v1/cron/describe?expr=0+*/6+*+*+*");
const data = await resp.json();
console.log(data.description); // "Every 6 hours"
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Rate limits

All free endpoints are rate-limited to prevent abuse (typically 30-60 requests per minute per IP). More than enough for development and testing.

Full API docs

Each product has Swagger UI and ReDoc:

These are all part of Anethoth, a collection of developer tools I'm building. If you find any of them useful, I'd love to hear about it in the comments.

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