// free · private · no sign-up · curl-friendly
Developer tools for the parts of the internet that break.
DNS, SSL/TLS, HTTP, email, networking, encoding and debugging. Real
protocol-level checks from a real server, answered in plain text for
curl and JSON when you ask. Nothing you look up is stored.
Check your domain.
One check across DNS, SSL/TLS, HTTP and email. Four real probes run in parallel, graded A to F, every finding explained, with a link into the full tool for the detail.
- DNSA, AAAA, nameservers, CAA
- SSL/TLSchain, expiry, TLS 1.3, legacy protocols
- HTTPHTTPS redirect, HTTP/2, compression, security headers
- EmailMX, STARTTLS, SPF, DKIM, DMARC
The ones you'll use most.
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server-side
DNS lookup
A, AAAA, CNAME, MX, NS, TXT, SOA, CAA, SRV and PTR against Cloudflare, Google, Quad9 or your own resolver. TTLs, response codes, timings. Compare resolvers to check propagation.
Run a DNS lookup -
server-side
SSL/TLS certificate checker
A live handshake, not a CT search: full chain, missing intermediates, expiry, SANs, TLS 1.0 through 1.3, cipher, ALPN, OCSP stapling. Test a new certificate with a custom SNI.
Check a certificate -
server-side
Email deliverability checker
MX and STARTTLS, SPF parsed as a tree with the 10-lookup count, DMARC decoded, DKIM keys, MTA-STS, TLS-RPT, BIMI. A graded report on why mail lands in spam.
Check SPF, DKIM & DMARC -
server-side
HTTP header & redirect checker
Every redirect hop with its status, DNS/connect/TLS/TTFB/download timing per hop, final headers, HTTP/2, compression and a plain-English security header scorecard.
Inspect a URL -
in your browser
JSON formatter & viewer
Validate with a clear error, format or minify, sort keys, browse as a collapsible tree and edit keys and values in place. Nothing is uploaded.
Format some JSON -
in your browser
Hash & HMAC generator
SHA-256, SHA-512, MD5, SHA-1, CRC32 of text or a dropped file, HMAC with a key, hex or Base64, and a verifier that tells you which algorithm a checksum came from.
Generate a hash
Built by an infrastructure engineer
who got annoyed with bad infrastructure tools.
Most of these started as private pages I kept for my own day to day: checking a DNS change, reading a certificate chain, working out why an email landed in spam, staring at a redirect that should not be there. The public versions were scattered across ad-heavy sites, half of them wanting an account before they would answer a simple question, most of them guessing rather than checking.
So these do the real thing. The DNS tool sends real DNS queries. The SSL checker
opens a real TLS connection and reports what came back. The email checker follows
every SPF include. The HTTP checker follows each redirect on a fresh
connection and times every phase. The IP tool reads live BGP data and the registry's
own RDAP record instead of pretending to know your street. The browser-side tools never
send your data anywhere.
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- tools
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- things stored
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- Go binary
- Real protocol-level checksUDP/TCP DNS, live TLS handshakes, SMTP STARTTLS probes, hop-by-hop HTTP. What a client sees, not what a database says.
- Plain text for curl, JSON on requestEvery server-side tool is also a tiny API.
?format=jsonor anAcceptheader is all it takes. - Private by constructionNo accounts, no cookies, no stored results. Encoding, hashing, JSON and diff run entirely in your browser.
- Explained, not just flaggedEvery finding says what it means and what to change. The guides go deeper when you want the why.
- FastOne small Go binary, no frameworks, no build step. The same process serving this page runs the checks.
Browse by category.
Built by Kirk Diamond.
I'm a software engineer who has spent most of my career at the hard end of the stack: backend systems, edge platforms and network-layer code, mostly in Go, for some of the world's biggest brands. I have been a principal engineer and a CTO, and I still write the code.
I originally wrote these tools because I needed them myself. They run on the same kind of infrastructure I have spent years building, and every explanation on this site comes from having seen the thing break in production.
Guides to the next question.
Short, first-hand answers to the thing you want to know right after a tool has shown you something.