A curated list of falsehoods programmers believe in.
The logic of the world is prior to all truth and falsehood.
— Ludwig Wittgenstein
Falsehood articles are a form of commentary on a particular subject, and are
appreciated by the developer community at large for their effectiveness and
terseness. They’re a convenient written form to approach an unfamiliar domain
by dispelling myths, point out common pitfalls, show inconsistencies and
In a sense, Falsehood articles are a suite of wordy unit-tests covering
extensive edge-cases provided by real-world usage.
- Dates and Time
- Human Identity
- Phone Numbers
- Postal Addresses
- Software Engineering
- Falsehoods Programmers Believe – A
brief list of common falsehoods. A great overview and quick introduction into
the world of falsehoods.
- Falsehoods About Programming – A
humbling and fun list on programming and programmers themselves.
- Falsehoods About Falsehoods Lists – Meta
commentary on how these falsehoods shouldn’t be handled.
- Falsehoods About Music – False
assumption that might be made in codifying music.
- Falsehoods About Art – Common
misconceptions about art.
- Falsehoods About Online Shopping – Covers
prices, currencies and inventory.
- Falsehoods About Prices – Covers
currencies, amounts and localization.
- Falsehoods About IBANs – International
Bank Account Numbers are not immune to mistakes.
- Falsehoods About Economics – Economics
are not simple or rational.
- Falsehoods About Cars – Even
something as common as defining a car is full of pitfalls.
- 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.
- CLDR currency definitions – Currency
validity date ranges overlap due to revolts, invasions, new constitutions, and
slow planned adoption.
tax– A PHP 5.4+ tax management
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.
- Your Calendrical Fallacy Is Thinking… – List
covering intercalation and cultural influence, made by a community of iOS and
- Time Zone Database – Code and data that
represent the history of local time for many representative locations around
- The Long, Painful History of Time – Most
of the idiosyncrasies in time keeping can find an explanation in history.
- 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.
- $26,000 Overcollection by Labor Department – The
consequence of wrong calendar accounting.
yyyy, and why your year may be wrong – String
formatting of date is hard.
- 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.
- Falsehoods about Unix Time – Mind
the leap second!
- 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.
- 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.
- 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.
- Postdoc myths –
Lots of things are said, written and believed about postdoctoral researchers that are simply not true..
- I Knew How to Validate an Email Address Until I Read the RFC – Provides
intricate examples that are unsuspected valid email addresses according the
- 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.
- Falsehoods About Geography – Takes
on places, their names and locations.
- Falsehoods About Maps – Covers
coordinates, projection and GIS.
- 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 Gender: #1 & #2 – Gender
is part of human identity and has its own subtleties.
- 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.
- Falsehoods Programmers Believe About Families – You
can’t really define a family with strict rules.
- Personal Names Around the World – How
do people’s names differ around the world, and what are the implications for
- XKCD #327: Exploits of a Mom – Funny take on how
implementation of a falsehood might lead to security holes.
- 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.
- My name causes an issue with any booking! – Old
airline reservation systems considers the
Misterand drops it.
- HL7 v3 RIM – A
flexible data model for representing human names.
- Apple iOS
representations of the components of a person’s name.
- Falsehoods About Me – Issues at
the intersection of names and gender and internationalization.
On character encoding, string formatting, unicode and internationalization.
- Falsehoods About Language – Translating
a software from English is not as straightforward as it seems to be.
- Internationalis(z)ing Code – A
video about things you need to keep in mind when internationalizing your
- 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.
- Awesome Unicode – A curated list
of delightful Unicode tidbits, packages and resources.
- 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-1Assumptions – Most
programmers spend so much time with
Latin-1they forgets about other’s scripts
- Ode to a shipping label – Character
encoding is hard, more so when each broken layer of data input adds its own
- i18n Testing Data – Compilation of
real-word international and diverse name data for unit testing and QA.
- Big List of Naughty Strings – 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
- Falsehoods About Job Applicants – Assumptions
about job applicants and their job histories aren’t necessarily true.
- Falsehoods About Video – Cover
it all: video decoding and playback, files, image scaling, color spaces and
conversion, displays and subtitles.
- Falsehoods About Networks – Covers
TCP, DHCP, DNS, VLANs and IPv4/v6.
- 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.
attempt to validate hostnames in Python.
- Falsehoods About Phone Numbers – Covers
phone numbers, their representation and meaning.
international phone numbers. Also available for
- 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.
- Letter Delivered Despite No Name, No Address – Ultimate
falsehood about postal addresses: you do not need one.
- 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.
common C++ and Java library for parsing, formatting, and validating
international postal addresses.
addressing– A PHP 5.4+
addressing library, powered by Google’s dataset.
module to parse, normalize and render postal addresses.
address– Go library to validate
and format addresses using Google’s dataset.
- Falsehoods About Systems of Measurement – On
working with systems of measurement and converting between them.
- 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.
- Falsehoods About Versions – 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 File Paths – Diversity
of file-systems and OSes makes file paths a little harder than we might think
- Falsehoods About REST APIs – Pitfalls
to be mindful of when creating and documenting APIs.
- Falsehoods About CSVs – While
RFC4180 to exists, it is far from definitive and goes largely ignored.
- Falsehoods About Package Managers – Covers
package and their managers.
- Falsehoods About Testing – An
attempt to establish a list of falsehoods about testing.
- Popular misconceptions about
of a post on why file’s
mtimecomparison could be considered harmful.
- Falsehoods About Pagination – Why
your pagination algorithm is giving someone (possibly you) a headache.
- Rules for Autocomplete – Not
falsehoods per-se, but still a great list of good practices to implement
- Floating Point Math – “Your language isn’t
broken, it’s doing floating point math. (…) This is why, more often than
0.1 + 0.2 != 0.3.”
- Falsehoods About Search – Why
search (including analysis, tokenization, highlighting) is deceptively complex.
- Hi! My name is… – This talk
could have been named “falsehoods about usernames (and other identifiers)”.
- Myths about
are a few things about
/dev/randomthat are repeated again and
again. Still they are false.
- Myths about CPU Caches – Misconceptions
about caches often lead to false assertions, especially when it comes to
concurrency and race conditions.
- 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.
- Norway is not False – Norway’s ISO country code is also valid YAML for False.
- Falsehoods About Fonts – Assumptions
about typography on the web and in desktop applications.
- Truths programmers should know about case – A
complete reverse of the falsehoods format, on the topic of case (as in uppercase
and lowercase text).
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Content of this repository is licensed under the Creative Commons CC0 license.
To the extent possible under law, Kevin Deldycke
has waived all copyright and related or neighboring rights to this work.