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About this tool
Build Slack thread summary, recap and action-item prompts that fit Slack's 40,000 character message and 3,000 character block limits.
Slack AI Prompt Builder writes the prompt for a thread summary, channel recap, action-item list or escalation note, fixing the headings the answer must use and the number of bullets it may contain. It then sizes that answer against Slack's real limits — 40,000 characters in one message, 3,000 characters in a Block Kit section block and 50 blocks per message — so you find out before posting that a recap will not fit. It is for anyone who gets summaries back that are three times too long, attribute decisions to nobody, or quietly invent conclusions the thread never reached.
Open Slack AI Prompt Builder on AltFTool — it loads instantly in your browser.
Provide your input — an image, text, or data.
Let the tool analyze or generate the result.
Review, refine, and reuse the output wherever you need it.
Each task type forces the same section structure, so summaries stay comparable instead of drifting.
Bullets times words gives an estimated character count and the number of section blocks it needs.
Reminds the assistant that Slack uses *bold* and _italic_, not the ** and # of standard Markdown.
One Slack message holds up to 40,000 characters in its text field. If you post with Block Kit instead, each section block caps at 3,000 characters and a single message holds at most 50 blocks, so a long recap has to be split across blocks.
Slack renders mrkdwn, not standard Markdown. Bold is a single asterisk on each side (*bold*), italic is underscores (_italic_), strikethrough is tildes (~strike~) and there are no # headings. Assistants default to Markdown unless the prompt says otherwise, which is why this tool adds that instruction.
Tell it explicitly to list unresolved points as open questions and to say when a heading cannot be filled. A summary asked for a fixed set of headings will otherwise fabricate content for the empty ones, which is the most common failure in thread summarisation.
That depends on your employer's policy and the tool's data handling, not on this page. This builder never receives your messages — it only assembles the instruction text in your browser — but you should confirm your workspace rules before pasting internal threads into any external assistant.