I built an API monitor that catches silent failures — and here's what I've learned building in public

#showdev #buildinpublic #devops #api

The problem nobody talks about

Your API returns 200 OK.
Your monitor says healthy.
Your users are seeing broken data.

This is a silent failure — and it's more common than you think.

// HTTP 200 OK — but...
{
  "status": "ok",
  "data": null,
  "error": "DB_CONNECTION_FAILED"
}

Standard monitors check the status code and stop there.
They have no idea what's actually inside the response.

What I built

CheckAPI — API monitoring that validates the response body, not just the status code.

Four layers of detection:

1. Keyword validation
A string that must be present or absent in the response body.

Present: "status":"ok" must exist
Absent: "error" must not exist

2. Regex pattern matching
"status":\s*"(ok|healthy)"
"balance":\s*[1-9]\d*

3. JSONPath assertions
Up to 10 per monitor, AND/OR logic, 11 operators.
$.status equals "healthy"
AND $.database equals "connected"
AND $.errorCount less than 1

4. Header assertions
Validate Content-Type, X-Status, or any custom header.

Both Regex and JSONPath have live testers built into the dashboard.
Test your pattern against a real response before saving.

Everything that's live today

All HTTP methods (GET/POST/PUT/DELETE/PATCH/HEAD/OPTIONS)
Custom headers + request body
Heartbeat/Cron monitoring (64-char token + grace period)
Public Status Page (/status/{id}) — zero auth required
5 alert channels: Email, Slack, Telegram, Discord, Webhook
Response time percentiles (p50/p95/p99)
SLA reports (Pro/Business)
Maintenance windows
REST API access (Business plan)

Pricing

Plan	Price	Monitors	Interval	History
Free	$0	10	5 min	30 days
Starter	$5/mo	20	1 min	30 days
Pro	$15/mo	100	30 sec	90 days
Business	$49/mo	Unlimited	10 sec	365 days

Free plan: commercial use allowed. Forever. No credit card required.

Honest build in public numbers

Real users: 7
MRR: $0 (payments are live)
Solo founder from Seoul 🇰🇷
Stack: FastAPI + Celery + Redis + PostgreSQL → Railway / Next.js 14 → Vercel
Open source (MIT): github.com/JEONSEWON/CheckAPI

What's still missing

Team UI (API already done)
Multi-location checks
TCP/Port/DNS monitors
SLA Report PDF export

What I've learned

Getting a strong response to launch content is not the same as
validating that people will pay for your product.

I've had good engagement, real conversations, and zero conversions.

The hardest part isn't building the detection logic.
It's reaching developers who haven't been burned yet —
because they don't go looking for monitoring tools until something breaks.

Still figuring it out in public.

→ **[checkapi.io]
(https://www.checkapi.io/)