Sealed：放得下才封口的信封

一个能直接用的字数检查器，用三只信封来做：“X post”“Bluesky post”和“One text message”（一条短信）。只有文字真的放得下，信封才会封上红色火漆。

打开页面时已经放好一封示例信（“Running 10 minutes late — the train’s stuck outside Hongqiao…”）。第一秒内纸条滑进信封：X（125 / 280）和 Bluesky（125 / 300）合上并封蜡；短信信封合不上，纸条顶出信封盖，红色虚线以上露出的就是真正放不下的那段原文，下方写着 “Open · 55 over · sends as 2 texts”。为什么只有 70？一条虚线框直接点名：一个破折号和一个弯引号。短信里只要出现一个 GSM 字母表以外的字符，上限就从 160 变成 70。按 “Make it SMS-safe (swap 3)”，第三只信封当场以 125 / 160 封上。

每打一个字信封都会跟着变化。“Trim to fit” 会把超出的部分剪到放得下为止，不会把一个字符剪成两半；Undo 可以恢复。你打的字永远不会被悄悄改写，只有这些按钮会改动文字。emoji 换不掉，会标成 “can’t swap”，不会被偷偷删掉。可以复制文字；剪贴板被拦截等错误会直接显示并朗读。减少动态效果时直接显示最终状态。360 px 手机可用。不存储、不上传任何内容。

计数依据：X 直接用 X 开源的 twitter-text 3.1.0（未改动，打包进页面），链接算 23，大部分中日韩文字和 emoji 算 2。Bluesky 按帖子 schema 的两条线：300 个字素、3,000 字节（UTF-8）。短信按 GSM 03.38：160 个 7 位字符（分条时每条 153，€ ^ { } [ ] ~ | \ 各占 2）；一旦出现 Unicode 字符就是 70（分条 67）。局限：比 twitter-text 3.1.0 更新的 emoji 按该库的方式计数，可能与 X 线上不同；Bluesky App 可能会缩短长链接；没有处理各国短信的扩展字符表。

在线试用：https://boloop-works.pages.dev/works/sealed/

下载原型文件（zip，152 KB）：https://boloop-works.pages.dev/works/sealed/sealed.zip

实际设计说明

Design a small, genuinely useful character counter made of three envelopes — "X post" (280, counted with X's open-source twitter-text 3.1.0, bundled unmodified), "Bluesky post" (300 graphemes and 3,000 UTF-8 bytes, from the app.bsky.feed.post schema) and "One text message" (GSM 03.38: 160 7-bit characters, or 70 once a single Unicode character appears) — as a runnable single-page web app (plain HTML/CSS/JS, no backend, no build, English UI, local fonts, inline SVG favicon).

First second, desktop and 390 px phone: a sample letter is already in place. Paper slips slide into the envelopes; X and Bluesky close and get a red wax seal pressed on; the SMS envelope cannot close — its slip sticks out above the flap and the part above a red dashed fold line is the actual text that does not fit. Under it: "Open · 55 over · sends as 2 texts". A dashed panel names the culprits ("These 2 marks shrink one SMS from 160 to 70 characters: — ’") with one button: "Make it SMS-safe (swap 3)".

Operable: every keystroke moves the slips, opens/closes flaps and presses or lifts seals. Explicit buttons only ever change the text: "Make it SMS-safe" (swaps ’ ‘ “ ” — – … and no-break space for plain ones; emoji are listed as "can't swap"), "Trim to fit" per open envelope (cuts to fit, never inside a grapheme), and one-level Undo. Typing is never rewritten, there is no maxlength. Errors are visible and announced (role=alert): empty copy, blocked clipboard, browser without Intl.Segmenter. Status line (aria-live polite) settles 0.7 s after typing. Reduced motion: final state at once. Nothing is stored or sent.

Inspired by @binniebunnnies and @marcgmbh.