Some bookmarklets

Edit: For the “welcome to Stack Overflow” bookmarklet, go to this jsFiddle, hit Run, and then drag the resulting link to your bookmarks bar.

A custom tea timer for https://smithtea.com/pages/know-your-tea#brewing-instructions:

javascript:(function(){var timestr=window.prompt("Time in sec?","120"); if(timestr===null) /*Cancel*/ return; clock.stop(); clock.reset(); var t = +parseInt(timestr,10) || 0; /*https://stackoverflow.com/a/7540412/2877364*/ if(t<=0) return; clock.setTime(t); clock.start(); })();

A message I have found myself typing frequently on Stack Overflow: 🙂

javascript:!function(){var t=document.querySelector.bind(document),o=t(".edit-post");if(o){var e=t(".js-add-link.comments-link");if(e){e.click();var a=t('textarea[name="comment"]');a&&(a.value="Welcome to the site! Check out the [tour](https://stackoverflow.com/tour) and the [how-to-ask page](https://stackoverflow.com/help/how-to-ask) for more about asking questions that will attract quality answers. You can [edit your question]("+o.href+") to include more information.",a.scrollTop=a.scrollHeight,a.focus())}}}();

As compressed by https://jscompress.com/; non-minified is:

javascript:(function(){
 var qsel = document.querySelector.bind(document);
 var edit_link = qsel('.edit-post');
 if(!edit_link) return;
 var add_comment = qsel('.js-add-link.comments-link');
 if(!add_comment) return;
 add_comment.click();
 var textbox = qsel('textarea[name="comment"]');
 if(!textbox) return;
 textbox.value =
"Welcome to the site! Check out the [tour](https://stackoverflow.com/tour) "+
"and the [how-to-ask page](https://stackoverflow.com/help/how-to-ask) for "+
"more about asking questions that will attract quality answers. You can "+
"[edit your question](" + edit_link.href + ") to include more information."
 textbox.scrollTop = textbox.scrollHeight;
 textbox.focus();
})();

These are the first two I have written.  I  hope they are useful to you, or serve as helpful examples if you are writing your own bookmarklets!