Learn and verify
Guides
Direct explanations to understand the problem, avoid mistakes and use each tool with confidence.
Category
Data and text
- Base64 and UTF-8: encode accents and emoji correctlyLearn why btoa fails or produces mojibake with Unicode and how to convert UTF-8 text and Base64 without losing characters.
- Base64 for text, files, and Data URLs: what changesDistinguish UTF-8 text, file bytes, and Data URLs so you do not copy prefixes, lose media types, or interpret binary as text.
- Base64 is not encryptionDistinguish encoding, encryption, and hashing, and learn why anyone can recover Base64 text without a key.
- Base64 vs Base64URLLearn when to use + and / or - and _, how padding works, and why compact JWT segments use Base64URL.
- Common errors when writing JSONIdentify and fix invalid commas, quotes, comments, escapes, numbers, and closings with before and after JSON examples.
- Decoding a JWT does not verify its signatureLearn what a JWT decoder reveals, which checks are still missing, and why unverified claims must never authorize an action.
- Duplicate keys in JSON: what happens and how to avoid themLearn why repeated object names produce unpredictable results and how to catch data loss before converting JSON.
- encodeURI vs encodeURIComponent: which one to useChoose the right function for a complete URL or an individual value without breaking &, =, ?,
- How to convert a date and time to a Unix timestampConvert a complete date to Unix time by choosing UTC or local time and seconds or milliseconds deliberately.
- How to convert JSON to CSV safelyTurn arrays of objects into a table, preserve stable columns, and reduce formula risks when opening CSV in a spreadsheet.
- How to convert JSON to YAML without losing typesLearn how to convert JSON to YAML preserving strings, numbers, booleans, and nulls, with testable examples and compatibility limits.
- How to convert YAML to JSON without surprisesIdentify the compatible subset, preserve types, and detect comments, anchors, tags, or keys that JSON cannot represent.
- How to detect and fix a double-encoded URLRecognize patterns such as %2520, find the boundary that encoded twice, and remove one layer without activating hidden delimiters.
- How to escape quotes, backslashes, and newlines in JSONLearn how to represent quotes, backslashes, newlines, and Unicode characters inside a valid JSON string.
- How to fix invalid Base64: incorrect padding and lengthDiagnose Base64 padding, length, alphabet, and trailing-bit errors without hiding truncated or corrupted data.
- How to fix URIError: URI malformed in JavaScriptFind incomplete percent escapes, invalid UTF-8 bytes, and lone Unicode surrogates that cause URI malformed errors.
- How to read a line-by-line text diffInterpret additions, deletions, and replacements, and learn how whitespace and line endings affect a text comparison.
- How to validate JSON and locate an errorLearn how to find and correct the first syntax error in a JSON using line, column and context, without sending your data.
- How to verify a SHA-256 checksum without confusing integrity and authenticityCompare a SHA-256 checksum correctly, detect changed bytes, and understand why a matching hash alone does not authenticate a publisher.
- How to write YAML lists and objects at the correct levelLearn to combine YAML sequences and mappings, align list markers, and verify the equivalent JSON structure.
- How URL percent-encoding worksLearn which characters to encode in a URL component, how UTF-8 becomes percent triplets, and why + does not always mean space.
- ISO 8601 vs Unix timestamp: differences and usesCompare ISO 8601 date-time text with Unix timestamps, including offsets, precision, and equivalent representations of one instant.
- JSON object vs array: differences and which belongs at the rootDistinguish JSON objects from arrays, choose the right root structure, and avoid incompatible API and conversion contracts.
- JSON vs YAML: differences and when to use eachCompare syntax, types, comments, references, and interoperability to choose JSON or YAML for a specific job.
- JSON: null vs missing fields vs undefinedDistinguish an explicit null, an absent property, and JavaScript undefined to avoid silent changes in APIs and serialization.
- JWT exp, iat, and nbf time claims explainedConvert and distinguish the exp, iat, and nbf claims in a JWT without confusing decoding with security validation.
- Large numbers in JSON and precision lossPrevent identifiers and integers above 53 bits from changing while JSON is parsed, formatted, or converted in JavaScript.
- LF and CRLF in Git: how to avoid whole-file changesUnderstand why Git can mark an entire file as changed and define consistent line endings with .gitattributes.
- Negative Unix timestamps and dates before 1970Learn what a negative Unix timestamp means, how pre-epoch dates are calculated, and which storage limits to check.
- Quotes in YAML: single, double, or unquoted stringsLearn when to use single quotes, double quotes, or plain scalars in YAML and how they affect escapes, comments, and types.
- Repeated query string parameters: how to preserve every valueLearn how repeated parameters work, why plain objects lose values, and when to use getAll, append, or an ordered list.
- SHA-256 hashing vs encryptionLearn what a SHA-256 fingerprint proves, why it is not decrypted, and when it is insufficient for passwords or authentication.
- Spaces in URLs: %20 vs +Learn when a space becomes %20 or +, how to preserve a literal plus sign, and which encoding belongs to each context.
- Unix timestamp seconds vs millisecondsDistinguish 10-digit and 13-digit timestamps, convert units without moving the instant, and diagnose implausible dates.
- Unix timestamps and leap seconds: what the counter really measuresUnderstand why Unix time does not count leap seconds as separate instants and how that affects conversions and durations.
- Unix timestamps, UTC, and local timeSeparate an absolute UTC instant from its local representation and avoid time-zone and daylight-saving errors.
- UUID v4 structure, randomness, and collisionsRecognize the version and variant bits, understand the 122 random bits in UUID v4, and interpret uniqueness correctly.
- UUID v4 vs UUID v7: randomness, time ordering, and choosingCompare UUID v4 and v7, understand which bits carry randomness or time, and choose based on privacy, ordering, and database indexes.
- What is a Unix timestamp and how is it calculated?Understand what Unix time measures, where its epoch starts, and how elapsed seconds map to an exact UTC date.
- YAML anchors, aliases, and merge keysUnderstand YAML node reuse, why JSON does not retain references, and what to verify before converting merged mappings.
- YAML booleans: why yes, no, on, and off depend on the versionPrevent words such as yes, no, on, and off from changing between strings and booleans across YAML parsers and versions.
- YAML indentation: spaces, tabs, and common errorsLearn how YAML indentation defines structure, why tabs cannot indent a block, and how to find a value at the wrong level.
- YAML multiline strings: the difference between | and >Understand literal and folded YAML block scalars, chomping indicators, and how to preserve or join line breaks.
- Year 2038 problem: what happens to 32-bit Unix timestampsUnderstand the 2147483647 limit, the 2038 overflow date, and how to check whether a system still uses signed 32-bit time.
Category
Networking
- 169.254 IP address: APIPA, link-local, and how to fix itLearn why a device assigns itself a 169.254 IPv4 address, what link-local connectivity permits, and what to check when DHCP fails.
- CIDR vs subnet mask in IPv4Learn how a CIDR prefix converts to an IPv4 subnet mask, what each bit means, and when the two notations are equivalent.
- How many hosts are in an IPv4 subnet?Calculate total and usable IPv4 addresses from a CIDR prefix, including the correct treatment of /31 and /32.
- How to calculate a CIDR prefix from the required host countChoose the smallest IPv4 subnet for a host count and calculate host bits, prefix, mask, and capacity with examples.
- How to calculate an IPv4 subnet step by stepLearn how to obtain network, broadcast and host range from an IPv4 and a CIDR prefix, with a /27 example solved by hand.
- How to convert IPv4 to decimal, binary, and hexadecimalConvert the four octets of an IPv4 address to an unsigned 32-bit integer, hexadecimal, and binary with a verifiable example.
- How to split a /24 network into four /26 subnetsDivide an IPv4 /24 into four /26 blocks and calculate each network, usable host range, and broadcast address in a complete example.
- IPv4 /31 vs /32: differences, hosts, and use casesDistinguish a /31 point-to-point network from a /32 host route and understand the addresses, broadcast, and capacity of each.
- IPv4 network, broadcast, first and last host addressesDistinguish IPv4 subnet boundaries and calculate network, broadcast, and host range with a worked /27 example.
- IPv4 wildcard masks explainedCalculate the inverse of an IPv4 subnet mask, interpret its bits, and avoid treating a wildcard as an IP address.
- Mbps and MB/s: differences and transfer timeDistinguish megabits per second from megabytes per second and learn to estimate how long a transfer takes with correct units.
- Private, CGNAT, and public IPv4 addressesIdentify RFC 1918 addresses and the shared CGNAT range, avoid mixing them up, and check other special-purpose IPv4 blocks.
Category
Embedded and electronics
- GB and GiB: differences and how to convert themLearn why gigabytes and gibibytes are not the same amount, how to convert them, and how to interpret the displayed capacity.
- How to calculate a resistor for an LEDCalculate a limiting resistor for one or more LEDs, choose a commercial value and check tolerance and power.
- How to convert binary to decimal step by stepConvert a binary integer to decimal by adding powers of two, with a fully worked example and an exact reverse check.
- How to convert decimal to hexadecimal step by stepConvert a decimal integer to hexadecimal by dividing by 16, interpreting remainders, and checking the exact result.
- How to read a resistor color codeLearn how to orient and decipher 4, 5 and 6 band resistors, with examples of value, tolerance and thermal coefficient.
- What is a CRC and how to choose its parametersUnderstand what a CRC detects, why the CRC-16 name is not enough, and how to choose polynomial, init, reflection, xorout, and byte order.