Slack Block Kit

Convert generative UI trees to Slack Block Kit payloads and decode block_actions interactions back into $action payloads.

API Reference

decodeBlockAction

Decodes one structural entry from a Slack block_actions payload.

decodeBlockAction

action : unknown

Converts Slack Block Kit JSON back into a generative-ui IR tree, inverting toSlackBlocks. Accepts a blocks array or a { blocks } wrapper; malformed input resolves to an empty node list plus a warning, and an unrecognized block or action element is skipped with a "dropped" warning. Every array read along the way (blocks, fields, options, elements, cards, rows, cells) is bounded to its site's cap before it is mapped over, so a hostile array (sparse or proxied with a fabricated length) is clamped with a "clamped" warning instead of stalling the event loop. Never throws.

The Slack shape is lossier than the IR, so some information cannot be recovered: a context block's elements always decode as Caption (the original Badge vs Caption distinction does not survive the round trip), a button's buttonStyle is only recovered for the primary/danger Slack styles, a native alert block's title and description merge into a single description string, and a card's layout collapses to its title, a flat children list (image, then text, then caption, in that order), and confirm/cancel footer buttons. A section field's label and value are split on the first *+newline delimiter, so a label or value that itself contains that exact delimiter cannot be split back unambiguously. A data-table cell that Slack carries as raw_text always decodes as a string, even when its text is the stringified form of a boolean, since the Slack shape does not distinguish a boolean from ordinary text.