Guides

Step-by-step instructions for a specific task, with a worked example.

• How to Format JSON Turn minified or broken JSON into something readable, and fix it when it will not parse.
• How to Convert CSV to JSON Turn a spreadsheet export into a clean JSON array, with the delimiter and header options that matter.
• How to Remove Duplicate Lines De-duplicate a list while keeping its order, with the case and whitespace options that decide what counts as a duplicate.
• How to Check DNS Records Look up A, MX, TXT and NS records for a domain, and read what they actually tell you.
• How to Decode a JWT Read the header and payload of a JSON Web Token, check its expiry, and understand why decoding is not verifying.
• How to Test a Regular Expression Build and debug a regex against real sample text, read the capture groups, and avoid the patterns that hang.
• How to Check HTTP Redirects Trace a URL through every hop to its destination, and tell a permanent redirect from a temporary one.
• How to Generate a Secure Password Produce a genuinely random password or passphrase, and understand what actually makes one strong.
• How to Convert XML to JSON Turn an XML document or feed into JSON, and handle the attributes and repeated elements that make it lossy.
• How to Hash Text with SHA-256 Produce a SHA-256 digest, compare it against a published checksum, and know when SHA-256 is the wrong tool.
• How to Compare Two Lists Find what two lists share and what only one of them has, without a spreadsheet formula.
• How to Calculate a Subnet Read CIDR notation and work out the network, broadcast and usable host range.
• How to Convert JSON to SQL Turn a JSON array into INSERT statements, and the traps to avoid when you run them.
• How to Convert a Unix Timestamp Turn epoch seconds into a readable date, and avoid the milliseconds and time zone traps.
• How to URL Encode Text Percent-encode a value safely, and know when to encode the component rather than the whole URL.
• How to Fix Broken Characters in Text Diagnose mojibake, question marks and invisible characters, and repair the text.
• How to Make a Markdown Table Build a pipe table, set alignment, and handle the content Markdown tables cannot hold.
• How to Debug an API Request Work through a failing request in order, from the status code to the payload.
• How to Verify a Webhook Signature Reproduce an HMAC signature correctly, and find out why yours does not match.
• How to Write Meta Tags The head tags that actually matter, what to put in them, and the ones to ignore.
• How to Write a robots.txt Control crawling correctly, and understand what the file cannot do.
• How to Fix "Unexpected Token" JSON Errors What each JSON.parse error message actually means, and why the problem is usually the response rather than the parser.
• How to Fix CSV Files Broken by Excel Leading zeros stripped, dates reformatted, long numbers turned into scientific notation, and accents turned to mojibake.
• How to Fix Base64 Decoding Errors Padding, the URL-safe alphabet, stray whitespace and double encoding — the four reasons a decode refuses.
• How to Fix XML Parsing Errors Content is not allowed in prolog, unescaped ampersands, mismatched tags and undeclared entities.
• How to Fix JWT Signature and Expiry Errors Invalid signature, token expired, malformed token — what each rejection actually tells you.
• How to Write a Cron Expression The five fields, what the special characters mean, and the two mistakes that cause a job to run far more often than intended.
• How to Fix a Regular Expression That Hangs Catastrophic backtracking explained: why a pattern that works on short input freezes on slightly longer input.
• How to Escape JSON Strings Which characters must be escaped, how to embed JSON inside JSON, and why the backslashes multiply.
• How to Validate an Email Address Why the perfect regex is the wrong goal, and what to check instead.
• How to Generate TypeScript Types from JSON Turn a sample API response into interfaces, and fix what a single sample cannot tell you.
• How to Flatten Nested JSON Turn a deep document into single-level dot-notation keys, and know when flattening loses information.
• How to Convert an HTML Table to CSV Get a table off a web page and into a spreadsheet, including the merged cells that break the alignment.
• How to Read a User Agent String Why every browser claims to be Mozilla, and what you can and cannot conclude from the string.
• How to Choose the Right MIME Type What a Content-Type header actually decides, and the mismatches that make browsers download files instead of showing them.
• How to Use Data URIs Embed an image or font directly in your markup, and know the size at which it stops being worth it.

What actually differs between two formats or algorithms, and which to pick.

• JSON vs YAML Which to use for configuration and which for data interchange, and the YAML gotchas worth knowing.
• JSON vs XML Why JSON replaced XML for most APIs, and the cases where XML is still the better answer.
• CSV vs TSV Why a tab separator avoids most quoting problems, and when to use each.
• SHA-256 vs MD5 Why MD5 is broken, what that actually means, and where it is still acceptable.
• SHA-256 vs SHA-512 Both are secure. Which to pick depends on hardware and interoperability, not strength.
• Base64 vs Encryption Base64 is an encoding, not a cipher. What it is actually for, and why it protects nothing.
• JSON Validator vs JSON Formatter Both parse your JSON. They differ in what they give you back and which one to reach for.
• UUID v4 vs v7 Random or time-ordered — which identifier version to use, and why it affects your database.
• UTF-8 vs UTF-16 Two encodings of the same character set, and why string lengths disagree between languages.
• Hashing vs Encryption One-way versus two-way, and why using the wrong one is a security bug.
• Bcrypt vs Argon2 Which password hashing function to use now, and whether an existing bcrypt store needs replacing.
• JWT vs Session Cookies Stateless tokens or server-side sessions — and why revocation is the deciding factor.
• CSV vs JSON Flat tables or nested structures — which format suits the data and the reader.
• Minification vs Compression Two different savings that stack — and why compression does most of the work.
• Character Count vs Word Count Which measure a platform uses, why they disagree, and when the difference bites.
• noindex vs robots.txt Blocking a page and removing it from search are different things — and using the wrong one backfires.
• URL Encoding vs HTML Encoding Two escaping schemes for two different destinations, and what happens when you apply the wrong one.