The name is the button.

An agent writes the code now, and a human thumb hovers over Accept all a hundred times a day. The honest question of this decade is what, exactly, you just accepted. So I read the diff.

Eight years as a backend engineer in Stockholm, back in Tokyo since 2023, and I still ship something small most nights, usually badly. My one rule: the only real review of a model is the thing you built with it. That is why there is no leaderboard on this site.

Around a hundred and forty sources come through — the labs' own posts, the papers, the tools, the runtimes and languages nobody is watching yet, the chip under the demo, and the newsletters people actually forward. What is moving gets counted so the week reads at a glance, and every few days I explain one mechanism in plain words.

A story here is a headline, a short excerpt, one image and the link to whoever wrote it. We never reproduce the post; the images belong to their authors. A post written in Japanese appears in Japanese, exactly as it was published, and the link goes to the original.

— Yuki Halvorsen, Tokyo

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MCP のエラーは2種類：プロトコルエラーと isError の使い分け

10.29

MCP（Model Context Protocol）のサーバーを作ると、最初につまずくのが「エラーをどう返すか」です。仕様には失敗の返し方が2種類あり、混ぜるとモデルが自分で直せなくなります。この記事では、公式仕様（2026-07-28 版、2026-10-28 に確認）に沿って、2種類の違いと使い分けを小さなコードで確かめます。

MCP, skills & tools

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MCP のエラーは2種類：プロトコルエラーと isError の使い分け

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