A birthday gift for a programmer
A birthday gift for a programmer can be the program they will not stop quoting. Give that one, as bars on a mug or a white tee.
Give the reference they already repeat
A birthday gift for a software engineer is personal, which means the category is a trap. Skip the generic coder mug. Listen for the citation. If they quote the Zen, the gift is Zen of Python, Tim Peters, PEP 20, this.py, PSF notice on the page. If they argue about a magic number in a game engine, the gift is Quake III inverse square root. Greg Walsh wrote it. The constant is 0x5f3759df. Say the name Walsh if you write a card. The miscredit is widespread, and a birthday is a good day to be the person who looked it up.
A birthday gift for a coder who follows money and protocols is Bitcoin halving. GetBlockSubsidy starts at 50 BTC and cuts that reward in half every 210,000 blocks. Satoshi Nakamoto and Bitcoin Core, MIT notice on the page. A birthday gift for a developer who came up on feeds and browsers might be RSS 1.0 or jQuery. Aaron Swartz was one author of RSS 1.0, at 14, with the RSS-DEV group in December 2000. He did not invent RSS alone. John Resig released jQuery in 2006. Both notices stay on the page.
A piece from the year they care about
Some people date themselves by a paper. Attention is the 2017 piece, Vaswani and co-authors, Attention Is All You Need. The bars are an original sketch of scaled dot-product attention, not a figure from the paper. A lawyer cleared that distinction. Give it to someone who entered the field through that door, not to someone who merely uses a chatbot.
The same test works backward. RSS is a gift for someone who misses the old web and can say why. The Zen is a gift for someone who likes a rule stated as a joke. You are matching a habit, not a demographic. Which piece to give is there if you have the habit and not the title of the file.
Desk or shirt, then stop
Ask one practical question. Do they drink at the desk, or do they wear a white tee? Both take the same artwork. Redbubble prints and ships to the EU and the US. Buy one. A birthday is a single object plus the fact that you knew which program.
Do not explain the piece at the table unless they ask. The page names the author, the year, and the notice. A toast that recites a license is how a good gift becomes a presentation. Hand them the mug. If you say one sentence, say the name of the person who wrote it.
A birthday gift for a developer who is about to change jobs can wait a month and become a goodbye. If the party is the party, stay with the reference they quote. The job change has its own page, and its own tone.