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😱 Falsehoods Programmers Believe in

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[ Daily / Weekly / Overview ]

Oct 12 - Oct 18, 2026

Business

• Things Many People Find Too Obvious To Have Told You Already - Reads like a list of falsehoods about the tech business: “There is no hidden reserve of smart people who know what they're doing, anywhere. Not in government, not in science, not in tech, (…) nowhere.”

Sep 28 - Oct 04, 2026

Geography

• Enclave and exclave - “Residing in an enclave within another country has often involved difficulties in such areas as passage rights, importing goods, currency, provision of utilities and health services, and host nation cooperation.” None of these attributes follows from a country code.

Software Engineering

• What every software engineer should know about search - A better sourced article on the difficulty of implementing search engines.

Aug 10 - Aug 16, 2026

Dates and Time

• “I'm going to a commune in Vermont and will deal with no unit of time shorter than a season.” - Is the note left on his terminal by a quitting engineer in the 70s, after too much effort toiling away on sub-second timing concerns. Source: The Soul of a New Machine.

May 04 - May 10, 2026

Internationalization

• Awesome Unicode (⭐986) - A curated list of delightful Unicode tidbits, packages and resources.

Phone Numbers

• Falsehoods about Phone Numbers (⭐18k) - Covers phone numbers, their representation and meaning.

• libphonenumber - 🆓 Google's common Java, C++ and JavaScript library for parsing, formatting, and validating international phone numbers. Also available for C# (⭐924), Objective-C (⭐2.4k), Python (⭐3.8k) and PHP (⭐5.1k).

Postal Addresses

• libaddressinput - 🆓 Google's common C++ and Java library for parsing, formatting, and validating international postal addresses.

Apr 20 - Apr 26, 2026

Postal Addresses

• Letter Delivered Despite No Name, No Address - Ultimate falsehood about postal addresses: you do not need one.

Dec 01 - Dec 07, 2025

Business

• “The system can’t handle a billion dollars” - Insane compensation at Meta in the middle of the AI-boom breaks ERPs.

Jul 21 - Jul 27, 2025

Business

• Decimal Point Error in Etsy's Accounting System - The importance of types in accounting software: missing the decimal point ends up with 100x over-charges.

• Twenty five thousand dollars of funny money - Same error as above at Google Ads, or the danger of separating your pennies from your dollars, where $250 internal coupons turned into $25,000. My advice: get rid of integers and floats for monetary values. Use decimals. Or fallback to strings and parse them, don't validate.

Dates and Time

• ISO-8601, YYYY, yyyy, and why your year may be wrong - String formatting of date is hard.

• Why is subtracting these two times (in 1927) giving a strange result? - Infamous Stack Overflow answer about both complicated historical timezones, and how historical dates can be re-interpreted by newer versions of software.

Geography

• Falsehoods about Maps - Covers coordinates, projection and GIS.

• Falsehoods about Weather - Weather is location-dependent, and so full of edge-cases.

Networks

• Falsehoods about Networks - Covers TCP, DHCP, DNS, VLANs and IPv4/v6.

Transportation

• Falsehoods about Aviation - Aviation data are less normalized than you might think.

• My name causes an issue with any booking! - Old airline reservation systems considers the MR suffix as Mister and drops it.

Apr 28 - May 04, 2025

Software Engineering

• Falsehoods about CVE - CVE ≠ vulnerability (and 36 other confusions).

Mar 10 - Mar 16, 2025

Internationalization

• Falsehoods about Language - Additional cases to complement the previous article.

Feb 17 - Feb 23, 2025

Software Engineering

• Falsehoods about null pointers - Null pointers are even more cursed than pointers in general, and provenance already makes pointers quite complicated.

• Falsehoods about Digital Object Identifiers (DOIs) - False conceptions about the identifiers that are used to identify and link research outputs (and a lot of other things).

Nov 11 - Nov 17, 2024

Software Engineering

• Facts about State Machines - State machines are often misunderstood and under-applied.

Jul 01 - Jul 07, 2024

Meta

• Falsehoods about Falsehoods Lists - Meta commentary on how these falsehoods shouldn't be handled.

Internationalization

• Unicode misconceptions - A collection of falsehoods on case, encodings, string length, and more.

Software Engineering

• Falsehoods about Event-Driven Systems - Misconceptions about event driven systems and message passing.

Apr 15 - Apr 21, 2024

Web

• Falsehoods about HTML - “Web is beautiful. Web is ugly. Web is astonishing. A part of this appeal is HTML, with its historical quirks.”

• The Hidden Complexity of Downloading Favicons, Told in 15+ Edge Cases - Downloading that little icon you see in you browser tabs should be a simple exercise. It turned out to be a lot more complicated than you think. Be vigilant that you are not shaving a Yak.

Mar 18 - Mar 24, 2024

Emails

• libvldmail - 🆓 A library that implements RFC-based checks for e-mail addresses.

Nov 06 - Nov 12, 2023

Internationalization

• Localization Failure: Temperature is Hard - You cannot localize temperature differences as-is.

Postal Addresses

• UK Address Oddities - Quirks extracted from a list of most residential property sales in England and Wales since 1995.

Jun 12 - Jun 18, 2023

Geography

• Top 5 most insane kanji place names in Japan - “There's one special group of kanji that's hard even for Japanese people to read: place names.”

Apr 17 - Apr 23, 2023

Software Engineering

• The weird world of Windows file paths - “On any Unix-derived system, a path is an admirably simple thing: if it starts with a /, it's a path. Not so on Windows.”

Mar 06 - Mar 12, 2023

Postal Addresses

• Why doesn't Costa Rica use real addresses? - Costa Rican uses an idiosyncratic system of addresses that relies on landmarks, history and quite a bit of guesswork.

• USPS Postal Addressing Standards - Describes both standardized address formats and content.

Jan 30 - Feb 05, 2023

Cryptocurrency

• Falsehoods about Ethereum - Misconceptions and common pitfalls in contract programming.

Jan 09 - Jan 15, 2023

Software Engineering

• The yaml document from hell - YAML is full of obscure complexity like accidental numbers and non-string keys.

Dec 19 - Dec 25, 2022

Networks

• IDN is crazy - International characters in domain names mean support of homographs and heterographs.

Dec 12 - Dec 18, 2022

Transportation

• The Maddening Mess of Airport Codes - Having multiple international and national agencies trying to reconcile history, practicality and logistics makes codes follow arcane rules.

Dec 05 - Dec 11, 2022

Business

• Minutiae of company names - How the rules of the State of Delaware and the IRS does not intersects.

Software Engineering

• Falsehoods about Undefined Behavior - Invoking undefined behavior can cause anything to happen, for a much broader definition of "anything" than one might think.

• I am endlessly fascinated with content tagging systems - There are edge-cases even in tagging systems which are supposed to be barebone.

Aug 29 - Sep 04, 2022

Emails

• Falsehoods about Email - On addresses, content and delivery.

Jun 20 - Jun 26, 2022

Business

• Falsehoods about Online Shopping - Covers prices, currencies and inventory.

Geography

• Falsehoods about Geography - Takes on places, their names and locations.

Internationalization

• Falsehoods about Plain Text - Plain text can't cut it, which makes Unicode even more incredible for its ability to just work well.

• Falsehoods about text - Practical examples illustrating Unicode normalization, ligatures, surrogate pairs, character widths, and grapheme cluster pitfalls in substring operations.

Apr 25 - May 01, 2022

Dates and Time

• The Long, Painful History of Time - Most of the idiosyncrasies in timekeeping can find an explanation in history.

• How to choose between UT1, TAI and UTC - Depends on your priorities between SI seconds, earth rotation sync, leap seconds avoidance.

• Critical and Significant Dates - From Y2K to the overflow of 32-bit seconds from Unix epoch, a list of special date to watch for depending on the system.

Software Engineering

• Rules for Autocomplete - Not falsehoods per se, but still a great list of good practices to implement autocompletion.

Apr 04 - Apr 10, 2022

Multimedia

• Horrible edge cases to consider when dealing with music - Music catalogs data are full of crazy stuff.

• MusicBrainz database schema - An open-source project and database that seems to have solved the complexity of music catalog management.

• DDEX - The industry standard for music metadata, including archiving, sound recording, sales and usage reporting, royalties and license deals.

• Apple Music Style Guide - Quality insurance guidelines to format music, art, and metadata to increase discoverability.

Mar 28 - Apr 03, 2022

Dates and Time

• Falsehoods about Unix Time - Mind the leap second!

• $26,000 Overcollection by Labor Department - The consequence of wrong calendar accounting.

Human Identity

• Falsehoods about Gender: #1 & #2 - Gender is part of human identity and has its own subtleties.

• XKCD #327: Exploits of a Mom - Funny take on how implementation of a falsehood might lead to security holes.

Software Engineering

• Hi! My name is… - This talk could have been named falsehoods about usernames (and other identifiers).

Jan 10 - Jan 16, 2022

Business

• CLDR currency definitions (⭐1.2k) - 🆓 Currency validity date ranges overlap due to revolts, invasions, new constitutions, and slow planned adoption.

Nov 08 - Nov 14, 2021

Transportation

• Falsehoods about Airline Seat Maps - Airline seat maps are far more complex than just neat rows and columns of seats.

Oct 18 - Oct 24, 2021

Dates and Time

• RFC-3339 vs ISO-8601 - An giant list of formats from the two standards, how they overlaps, and live examples.

Oct 04 - Oct 10, 2021

Software Engineering

• Falsehoods about Package Managers - Covers package and their managers.

Sep 20 - Sep 26, 2021

Web

• Falsehoods about REST APIs - Pitfalls to be mindful of when creating and documenting APIs.

Sep 06 - Sep 12, 2021

Video Games

• The Door Problem - All the things you have not considered implementing for your doors in games.

Aug 30 - Sep 05, 2021

Emails

• Your E-Mail Validation Logic is Wrong - A summary of the various, surprising things that are allowed in an email address.

Geography

• I Hate Coordinate Systems - A guide for geospatial practitioners on diagnosing and fixing common issues with coordinate systems.

Software Engineering

• Falsehoods about garbage collection - Misconceptions about the predictability and performance of garbage collection.

Jun 28 - Jul 04, 2021

Web

• URLs: It's complicated… - There's a lot of components in an URL, and all have their own logic.

Feb 08 - Feb 14, 2021

Meta

• Falsehoods about Programming - A humbling and fun list on programming and programmers themselves.

Arts

• Falsehoods about Music - False assumption that might be made in codifying music.

• Falsehoods about Art - Common misconceptions about art.

Business

• Falsehoods about Prices - Covers currencies, amounts and localization.

• Falsehoods about IBANs (⭐509) - International Bank Account Numbers are not international.

• Falsehoods about Economics - Economics are not simple or rational.

Cryptocurrency

• Falsehoods about Bitcoin (⭐85) - A list of mistaken perspectives on Bitcoin.

Dates and Time

• Falsehoods about Time - Seminal article on dates and time.

• More Falsehoods about Time - Part. 2 of the article above.

• Falsehoods about Time and Time Zones - Another takes on time-related falsehoods, with an emphasis on time zones.

• Critique of Falsehoods about Time - Takes on the first article above and provides an explanation of each falsehood, with more context and external resources.

• Falsehoods about Time Zones - Has some nice points regarding the edge-cases of DST transitions.

Human Identity

• Falsehoods about Names - The article that started it all.

• Falsehoods about Names – With Examples - A revisited version of the article above, this time with detailed explanations.

• Falsehoods about Biometrics - Fingerprints are not unique.

• Falsehoods about Families - You can't really define a family with strict rules.

• Falsehoods about Me - Issues at the intersection of names and gender and internationalization.

Internationalization

• Falsehoods about Language - Translating a software from English is not as straightforward as it seems to be.

Management

• Falsehoods about Job Applicants - Assumptions about job applicants and their job histories aren't necessarily true.

Multimedia

• Falsehoods about Video - Cover it all: video decoding and playback, files, image scaling, color spaces and conversion, displays and subtitles.

Postal Addresses

• Falsehoods about Addresses - Covers streets, postal codes, buildings, cities and countries.

• Falsehoods about Residence - It's not only about the address itself, but the relationship between a person and its residence.

Science

• Falsehoods about Systems of Measurement - On working with systems of measurement and converting between them.

Society

• Falsehoods about Political Appointments - Designing election systems has its own tricks.

• Falsehoods about Women In Tech - Myth about women in STEM (Science, Technology, Engineering, Math) industries.

Software Engineering

• Falsehoods about Versions (⭐69) - Attributing an identity to a software release might be harder than thought.

• Falsehoods about Build Systems - Building software is hard. Building software that builds software is harder.

• Myths about CPU Caches - Misconceptions about caches often lead to false assertions, especially when it comes to concurrency and race conditions.

• Falsehoods about CSVs - While RFC4180 to exists, it is far from definitive and goes largely ignored.

• Falsehoods about Testing - An attempt to establish a list of falsehoods about testing.

• Falsehoods about Search - Why search (including analysis, tokenization, highlighting) is deceptively complex.

• Falsehoods about Pagination - Why your pagination algorithm is giving someone (possibly you) a headache.

• Myths about File Paths - Diversity of file-systems and OSes makes file paths a little harder than we might think of.

• Myths about /dev/urandom - There are a few things about /dev/urandom and /dev/random that are repeated again and again. Still they are false.

Typography

• Falsehoods about Fonts (⭐111) - Assumptions about typography on the web and in desktop applications.

Dec 14 - Dec 20, 2020

Meta

• Falsehoods Programmers Believe - A brief list of common falsehoods. A great overview and quick introduction into the world of falsehoods.

Business

• tax - 🆓 A PHP 5.4+ tax management library.

Dates and Time

• Your Calendrical Fallacy Is Thinking… - List covering intercalation and cultural influence, made by a community of iOS and macOS developers.

• Time Zone Database - 🆓 Code and data that represent the history of local time for many representative locations around the globe.

• You Advocate a Calendar Reform - Your idea will not work. This article tells you why.

• So You Want to Abolish Time Zones - Abolishing timezones may sound like a good idea, but there are quite a few complications that make it not quite so.

• The Problem with Time & Timezones - A video about why you should never, ever deal with timezones if you can help it.

• UTC is Enough for everyone, right? - There are edge cases about dates and time (specifically UTC) that you probably haven't thought of.

• Storing UTC is not a silver bullet - “Just store dates in UTC” is not always the right approach.

Education

• Falsehoods CS Students (Still) Believe Upon Graduating - A list of things (not only) computer science students tend to erroneously and at times surprisingly believe even though they (probably) should know better.

Emails

• I Knew How to Validate an Email Address Until I Read the RFC - Provides intricate examples that are unsuspected valid email addresses according the RFC-822.

• So you think you can validate email addresses (FOSDEM 2018) - Presentation of edge-case email addresses and why you should not use regex to parse them.

Human Identity

• Gay Marriage: The Database Engineering Perspective - How to store a marriage in a database while addressing most of the falsehoods about gender, naming and relationships.

• Personal Names Around the World - How do people's names differ around the world, and what are the implications for the Web?

• Hello, I'm Mr. Null. My Name Makes Me Invisible to Computers - Real-life example on how implemented falsehood has negative impact on someone's life.

• HL7 v3 RIM - A flexible data model for representing human names.

• Apple iOS NSPersonNameComponentsFormatter - Localized representations of the components of a person's name.

Internationalization

• Internationalis(z)ing Code - A video about things you need to keep in mind when internationalizing your code.

• Minimum to Know About Unicode and Character Sets - A good introduction to unicode, its historical context and origins, followed by an overview of its inner working.

• Dark corners of Unicode - Unicode is extensive, here be dragons.

• Let's Stop Ascribing Meaning to Code Points - Dives deeper in Unicode and dispels myths about code points.

• Breaking Our Latin-1 Assumptions - Most programmers spend so much time with Latin-1 they forgets about other's scripts quirks.

• Ode to a shipping label - Character encoding is hard, more so when each broken layer of data input adds its own spice.

• i18n Testing Data (⭐70) - 🆓 Compilation of real-word international and diverse name data for unit testing and QA.

• Big List of Naughty Strings (⭐48k) - 🆓 A huge corpus of strings which have a high probability of causing issues when used as user-input data. A must have set of practical edge-cases to test your software against.

Networks

• Fallacies of Distributed Computing - Assumptions that programmers new to distributed applications invariably make.

• There's more than one way to write an IP address - Some parts of the address are optional, mind the decimal and octal notations, and don't forget IPv6 either.

Postal Addresses

• The Bear with Its Own ZIP Code - Smokey Bear has his own ZIP Code (20252) because he gets so much mail.

• Regex and Postal Addresses - Why regular expressions and street addresses do not mix.

• addressing - 🆓 A PHP 5.4+ addressing library, powered by Google's dataset.

• postal-address - 🆓 Python module to parse, normalize and render postal addresses.

• address - 🆓 Go library to validate and format addresses using Google's dataset.

Software Engineering

• Popular misconceptions about mtime - Part of a post on why file's mtime comparison could be considered harmful.

• Floating Point Math - “Your language isn't broken, it's doing floating point math. (…) This is why, more often than not, 0.1 + 0.2 != 0.3.”

Typography

• Truths programmers should know about case - A complete reverse of the falsehoods format, on the topic of case (as in uppercase and lowercase text).

Nov 16 - Nov 22, 2020

Postal Addresses

• Parsing the Infamous Japanese Postal CSV - “I saw many horrors, but I've never seen this particular formatting choice anywhere else.”

Nov 02 - Nov 08, 2020

Business

• Characters < and > in company names lead to XSS attacks - Because UK allows companies to be registered with special characters, a hacker leveraged them to register \"><SCRIPT SRC=MJT.XSS.HT></SCRIPT> LTD, but also ; DROP TABLE "COMPANIES";-- LTD, BETTS & TWINE LTD and SAFDASD & SFSAF \' SFDAASF\" LTD.

Jan 27 - Feb 02, 2020

Education

• Postdoc myths - “Lots of things are said, written and believed about postdoctoral researchers that are simply not true.”