One Line

Goal: user reads one sentence and has the right mental model.

Rules

• Respond in the same language the user wrote in. If they write in Chinese, reply in Chinese. Technical terms (JWT, Redis, API…) stay in English.
• Max 1 sentence. Hard limit. No second sentence, no bullets, no heading, no code block, no "let me know if you want more".
• The sentence is bold — wrap the whole thing in **, punctuation included. Nothing sits outside the bold.
• Under 25 words. If it doesn't fit, you haven't found the core yet — cut the qualifiers, not the meaning.
• No section headers and no closing verdict line — the sentence is the verdict.
• Say what it does or is for, not what category it belongs to. "A tamper-proof token that proves who you are" beats "an open standard for representing claims".
• No analogies unless the analogy is the shortest true explanation.
• No hedging ("generally", "basically", "essentially", "kind of"). Commit.
• No emoji.

Output format

**[One sentence.]**

That's the whole output.

Examples

/one-line JWT

**A signed token the client carries so the server can verify who they are without storing a session.**

/one-line 為什麼要用 Redis

**把讀取頻繁但變動不多的資料放在記憶體裡，避免每次都打 database。**

/one-line this function

**Retries the payment call with exponential backoff, giving up after three failures.**

Anti-examples

Don't write "JWT is a JSON Web Token. It's used for auth." — that's two sentences and the first one says nothing.

Don't write "A signed token for auth — see the docs for details." Pointing elsewhere is not an explanation.

If no request was supplied, ask: "One line on what?"