xkcd publishes each comic's title, image URL, and alt text as JSON. It sends no CORS headers, so from a browser these run through the PostTaco extension.
None — no key, no signup. Every example runs as-is.
Full reference: https://xkcd.com/json.html
curl https://xkcd.com/info.0.json{
"month": "9",
"num": 3301,
"link": "",
"year": "2026",
"news": "<br />Previously: <a href=\"https://xkcd.com/1644/\">Stargazing</a> • <a href=\"https://xkcd.com/2017/\">Stargazing 2</a> • <a href=\"https://xkcd.com/2274/\">Stargazing 3</a> • <a href=\"https://xkcd.com/3072/\">Stargazing 4</a>",
"safe_title": "Stargazing 5",
"transcript": "",
"alt": "The sun and the moon appear the same size in the sky, even though in real life the sun is more than twice as big. Some call this lucky alignment coincidence; others say it's proof that sometimes things can be the same size.",
"img": "https://imgs.xkcd.com/comics/stargazing_5.png",
"title": "Stargazing 5",
"day": "21"
}curl https://xkcd.com/927/info.0.json{
"month": "7",
"num": 927,
"link": "",
"year": "2011",
"news": "",
"safe_title": "Standards",
"alt": "Fortunately, the charging one has been solved now that we've all standardized on mini-USB. Or is it micro-USB? Shit.",
"img": "https://imgs.xkcd.com/comics/standards.png",
"title": "Standards",
"day": "20"
}