Network & API

All registered ALPN protocol identifiers — h2, h3, http/1.1 and more.

Convert request quotas into per-second, per-minute and spacing guidance.

Decode a Basic/Bearer/Digest Authorization header.

Look up well-known autonomous system numbers — Google, Cloudflare, ISPs…

Compose a tcpdump/BPF capture filter from form fields.

Validate CAA DNS record syntax (flag, tag, value).

Compose the HTTP Cache-Control header from directives.

Break a CIDR block into network, mask, broadcast, first/last and host count.

Simulate a browser CORS preflight without making any network requests.

Convert a curl command into JS fetch, PowerShell or .NET HttpClient code.

Common DHCP options with code, name and description.

Generate an RSA key pair and the matching DKIM DNS TXT record.

Build a DMARC TXT record with policy, alignment and reporting tags.

Parse a DMARC aggregate (RUA) XML report into a readable summary.

Resolve A, AAAA, MX, TXT, NS, CNAME and SOA records via DNS-over-HTTPS.

Convert between BIND-style DNS zone files and a JSON array of records.

Manual record of owned domains: registrar, renewal price, expiry, auto-renew, nameservers, notes.

Common DSCP code points with names, acronyms and PHB.

Look up a domain's live SPF, DKIM and DMARC DNS records and summarise the policy.

Parse email headers and Received hops.

Trace the Received hops, SPF/DKIM/DMARC results and DKIM signature of any email.

Validate email address syntax without contacting mail servers.

Fetch any URL and review its response headers + security headers.

Build a 'Range: bytes=…' header for HTTP byte-range requests.

Send any HTTP request and inspect the full response.

Core concepts behind HTTP/3 and QUIC, one short paragraph each.

Common ICMP type and code values with names and descriptions.

Classify any IPv4 / IPv6 address: public, private, loopback, link-local, multicast.

Convert IPv4 between dotted, integer, hex and binary.

Expand and compress IPv6 addresses; detect ULA.

Generate a random /48 IPv6 unique-local prefix (RFC 4193).

Compose JSON-RPC 2.0 requests, notifications and responses.

Identify the manufacturer for a MAC address's first 3 bytes.

Parse, classify and re-format a MAC / EUI-48 address.

Common mDNS / DNS-SD service type names with brief descriptions.

Compute MTU overhead, fragmentation and transfer time at various bandwidths.

Build OAuth 2 authorization URLs.

Preview how a page's OpenGraph / Twitter Card tags render on Facebook, Twitter, LinkedIn, Slack, Discord and iMessage.

Common QUIC frame types with their hex codes and purpose.

Generate random IPv4, IPv6 ULA or MAC addresses for mocking.

Resolve the PTR (reverse DNS) record for any IPv4 or IPv6 address.

Most-cited Internet RFCs by number with a one-line title.

Validate robots.txt and sitemap.xml together — including cross-checks (sitemap URL blocked by robots).

Persist HTTP request templates (method, URL, headers, body).

Parse a Set-Cookie header into structured fields.

Searchable reference of SMTP, FTP and IMAP response codes.

Common SNMP OIDs for system uptime, interfaces, CPU and memory.

Build an SPF TXT record from common include / ip4 / ip6 / mx mechanisms.

Build a DNS SRV record from service, proto, name, priority, weight, port and target.

Open a real SSH terminal in your browser — connect to a server with a password or private key and run a full interactive shell.

Saved hostnames probed over TLS to read leaf cert subject, issuer, validity window and SAN list.

Collapse a list of IPv4 CIDRs into the smallest covering set.

Split a CIDR block into 2ⁿ equal subnets.

Open a raw TCP socket to any host and port, send text and watch the reply — like netcat in your browser.

Decode a TCP control flag byte (CWR/ECE/URG/ACK/PSH/RST/SYN/FIN).

Test whether a TCP port is reachable from our server.

Reference of common TLS 1.2 / 1.3 cipher suites with strength notes.

Searchable reference for the TLS 1.2 / 1.3 handshake steps.

Saved list of URLs with manual on-demand HEAD/GET probes and a rolling check history.

Decode a User-Agent string into browser, engine, OS and device.

Build the magic UDP packet payload that wakes a host by MAC address.

Get a unique URL that records every inbound HTTP request — inspect headers, query and body.

Compute HMAC signatures for webhook bodies (Stripe, GitHub…).

Connect to any public ws:// or wss:// endpoint, send text/binary frames, watch the response.

Open a WebSocket, send one message and show the first response.

Look up domain registration data via RDAP-over-HTTPS.