Guides
Practical developer how-tos, no fluff.
Clear, step-by-step guides to the everyday dev tasks — formatting, encoding, validating and generating — each backed by a free tool that runs entirely in your browser.
How to Create a Glassmorphism Effect in CSS
Make a frosted-glass card with backdrop-filter, get the transparency and blur right, and copy CSS that works, without guessing at values.
Read guideHow to Count Tokens for GPT, Claude & Gemini
Tokens decide both whether a prompt fits and what it costs. Here is how to count them per model and turn the count into a cost estimate.
Read guideHow to Calculate a Subnet Mask
Turn a CIDR prefix into a mask, network and broadcast address, and host range. Here is the bit-level method, with worked examples.
Read guideHow to Calculate RAID Capacity
Usable space depends on the RAID level, not just the drives. Here is the capacity formula for each common level, with worked numbers.
Read guideHow to Check an SPF Record
Find a domain SPF record, read what each mechanism does, and catch the faults that break it — too many lookups, two records, a weak all policy.
Read guideHow to Check If an IP Is Blacklisted
Test an IP against the major DNS blocklists, read the verdict, and understand why some lists return no answer — plus what to do if you are listed.
Read guideHow to Check MX Records
Look up a domain's mail servers and read the priority order that decides which one is tried first. How MX records work and what an empty result means.
Read guideHow to Compress an IPv6 Address
RFC 5952 gives one correct short form for every IPv6 address. Here are the three rules, the :: tie-breaker, and worked examples.
Read guideHow to Convert an IP Address to Binary
An IPv4 address is 32 bits in disguise. Here is how to convert each octet to binary, and how the same bits read as an integer and hex.
Read guideHow to Convert IPv4 to IPv6
An IPv4 address has several IPv6 representations. Here is how the mapped, compatible and 6to4 forms are built, with worked hex examples.
Read guideHow to Create an SPF Record
An SPF record lists who is allowed to send mail as your domain. Here is how to build one that passes, with the limits that trip people up.
Read guideHow to Do a DNS Lookup
Check any domain's DNS records from your browser. What each record type means, how to read the TTL, and how to tell a cached answer from a live one.
Read guideHow to Expand an IPv6 Address
Expanding an IPv6 address means undoing :: and the dropped zeros. Here is the two-step method, with a worked example.
Read guideHow to Find the Vendor of a MAC Address
A MAC address carries the maker's identity in its first three bytes. Here is how to read it, and when the answer is hidden on purpose.
Read guideHow to Set Up DKIM
DKIM signs your mail with a private key and publishes the public key in DNS. Here is how to generate, publish and rotate a key without breaking delivery.
Read guideHow to Set Up DMARC
DMARC ties SPF and DKIM to your From address and tells receivers what to do on failure. Here is the monitor-first rollout that avoids losing real mail.
Read guideHow to Write a robots.txt File
A robots.txt tells crawlers where they may and may not go. Here is how to write one correctly, plus the trap that catches people who want to hide a page.
Read guideWhat Is a Unique Local IPv6 Address
A ULA is the IPv6 version of a private network range. Here is how the fd prefix, random global ID and /64 subnets work.
Read guideWhat Is CIDR Notation?
CIDR notation packs an address and a prefix length into one string like 192.168.0.0/22. Here is how to read it and what range it covers.
Read guideWhat Is Punycode
Punycode turns a domain like münchen.de into an ASCII xn-- label DNS can store. Here is how it works and why international domains need it.
Read guideWhat Is Reverse DNS
Reverse DNS turns an IP address back into a hostname through a PTR record. Here is how it works, why mail servers care, and how to check it.
Read guideHow to Generate CSS Gradients, Shadows & Glassmorphism
Tune gradients, shadows, border-radius and glassmorphism visually and copy production-ready CSS, no memorizing syntax.
Read guideHow to Generate Fake Test Data (JSON, CSV, SQL)
Design a schema, pick field types, set a row count, and export mock data as JSON, CSV or SQL without writing a script.
Read guideHow to Make a Beautiful Code Screenshot
Paste code, pick a theme and background, and export a sharp image for blog posts, docs and social, without taking an OS screenshot.
Read guideHow to Make an Open Graph Image for Social Sharing
Build a 1200x630 social preview card, export a PNG, and wire up the og:image and twitter:image tags so shared links look sharp.
Read guideHow to Visualize JSON as a Graph
See the shape of nested JSON as a node graph or tree, collapse branches, and copy the dot-path to any value.
Read guideHow to Decode and Verify a JWT
Read the header and claims, check exp and nbf, and understand what signature verification does — and why you should never decode tokens on a server you don't trust.
Read guideHow to Encode and Decode Base64
What Base64 actually does, when to reach for the URL-safe variant, and how to encode files as well as text — without uploading anything.
Read guideHow to Format and Validate JSON
Beautify messy JSON, catch the exact parse error, and know when to minify vs. pretty-print — without uploading your data anywhere.
Read guideHow to Generate a QR Code (with a Logo)
Add a logo and brand colors without breaking scannability, and pick PNG vs. SVG correctly for screen and print.
Read guideHow to Hash Text and Files (MD5, SHA-256)
Verify a file checksum, pick the right algorithm, and learn why MD5 and SHA-256 are the wrong tools for passwords.
Read guideHow to Test and Debug a Regular Expression
Flags, capture groups, greedy vs. lazy matching, and the small mistakes that make a regex match too much or nothing at all.
Read guideSkip the reading — just use the tools
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