lark-formatting

Build a JSON object with msg_type interactive containing a config, a header with a title and color template, and an elements array of markdown, hr, column_set, button, or note tags. Set wide_screen_mode to true so the card renders well on mobile.

Lark supports three message types: text for plain messages with basic markdown, interactive for CardKit JSON cards with buttons and columns, and post for legacy rich text. CardKit is recommended for any structured content like reports or alerts.

Both support markdown bodies, buttons, images, multi-column layouts, and dividers. Lark CardKit adds colored header templates but lacks input forms, while Slack Block Kit supports input blocks and has a roughly 40KB message limit versus Lark's 30KB.

Use the at tag in markdown content with the user's open ID, for example <at user_id="ou_xxx">@Alice</at>. In plain text messages you can use the @_user_1 syntax, where the number maps to the user's order in the chat.

Plain text messages are limited to roughly 30KB, and CardKit cards support a maximum of 50 elements per card. For larger reports, split the content across multiple cards instead of a single payload.

Avoid CardKit for simple direct messages where plain text suffices, since the JSON structure adds token overhead. Also use platform-specific formatters instead when delivering to Slack or WhatsApp rather than Lark.