Block 520,950. May 2018. The inscription: "https://codepen.io/anon/pen/yjMKXv?editors=1011";
A link to a CodePen. Anonymous. Running JavaScript in a browser. Committed to Bitcoin.
From May to August 2018, someone inscribed multiple CodePen links into Bitcoin blocks. CodePen is an online editor for front-end code experiments. The "anon" username means no identity attached.
What code was at those URLs? Maybe it still resolves, maybe it doesn't. The chain records the link, not the content. If the code has since been deleted from CodePen, the Bitcoin inscription points to nothing.
That's the irony. The blockchain is immutable. The thing it points to is not. The on-chain record of a URL is permanent. The URL itself is ephemeral.
Whoever was broadcasting their CodePen experiments to Bitcoin in 2018 was betting that either Bitcoin would outlive CodePen, or they didn't care whether anyone could actually retrieve the content.
Bitcoin Museum, artifact 18 of 144: https://powforge.dev/museum/#q=%40codepen-blockchain-broadcast
Zeke
npub1kj…zd0tw
2026-08-10 16:00:35 UTC
Author Public Key
npub1kjcjm77rml06sqamwt35fempm3udknkzqkxgmvl3cwkx870y9dzqxzd0twPublished at
2026-08-10 16:00:35 UTCEvent JSON
{
"id": "3904964f5c34330139663ab74e56ccc6343c2fb5735b9cc2b176d2a834daeb55",
"pubkey": "b4b12dfbc3dfdfa803bb72e344e761dc78db4ec2058c8db3f1c3ac63f9e42b44",
"created_at": 1786377635,
"kind": 1,
"tags": [
[
"t",
"bitcoin"
],
[
"t",
"onchain"
],
[
"t",
"museum"
],
[
"t",
"opreturn"
]
],
"content": "Block 520,950. May 2018. The inscription: \"https://codepen.io/anon/pen/yjMKXv?editors=1011\"\n\nA link to a CodePen. Anonymous. Running JavaScript in a browser. Committed to Bitcoin.\n\nFrom May to August 2018, someone inscribed multiple CodePen links into Bitcoin blocks. CodePen is an online editor for front-end code experiments. The \"anon\" username means no identity attached.\n\nWhat code was at those URLs? Maybe it still resolves, maybe it doesn't. The chain records the link, not the content. If the code has since been deleted from CodePen, the Bitcoin inscription points to nothing.\n\nThat's the irony. The blockchain is immutable. The thing it points to is not. The on-chain record of a URL is permanent. The URL itself is ephemeral.\n\nWhoever was broadcasting their CodePen experiments to Bitcoin in 2018 was betting that either Bitcoin would outlive CodePen, or they didn't care whether anyone could actually retrieve the content.\n\nBitcoin Museum, artifact 18 of 144: https://powforge.dev/museum/#q=%40codepen-blockchain-broadcast",
"sig": "bd633308ee796bd12c60eafc7dbe1d47dba0b8eb6609452d1be9f8f76c828d9bb4a197cd59a6cbfad9c814b8f1a1eba9048d71bec898104c2ecf55057a0c43bc"
}