# Laneboard Cumulative Flow

> Cumulative flow diagram of a kanban board: cards per list for every day, plus WIP and throughput. Rebuilds how many cards were in each list at the end of every day from the card history of a Laneboard board or a Trello export, draws the cumulative flow diagram and works out arrivals, finished cards, average work in progress and a Little’s law lead-time estimate.

Part of usefulweb.app (https://usefulweb.app/). Part of [Laneboard](https://laneboard.usefulweb.app/) (ownerApp: laneboard). Results are deterministic calculations from the inputs and the listed assumptions; the API returns exactly what the web page shows.

## Use it
- Human interface: https://laneboardcumulativeflow.usefulweb.app/ (interactive tool at https://laneboardcumulativeflow.usefulweb.app/tool)
- JSON API: POST https://laneboardcumulativeflow.usefulweb.app/api/v1/calculate with a JSON object of inputs (schema: https://laneboardcumulativeflow.usefulweb.app/api/v1/tool)
- OpenAPI: https://laneboardcumulativeflow.usefulweb.app/openapi.json
- MCP (Streamable HTTP): https://laneboardcumulativeflow.usefulweb.app/mcp - tool `laneboard_cumulative_flow`

## Inputs
- board (textarea): Board (JSON) - A Laneboard project or board file (.laneboard.json), a Laneboard share snapshot, or a Trello board export (JSON).
- boardFile (file): Board file (optional) - Used instead of the pasted text when given.
- boardName (text): Board (projects with several boards) - Board title or number (1 = first). Empty = the board that was open last.
- asOf (date): As of (date) - The day the numbers are counted for. Empty = today.
- from (date): From (date) - Empty = when the first card was created (at most 90 days back).
- to (date): To (date) - Empty = the “as of” date.

## Method
- For every day the tool replays each card’s history (created in a list, moved, archived, restored) up to midnight UTC at the end of that day and counts the cards per list. Archived cards leave the chart on the day they were archived.
- The chart stacks the lists with the last list (done) at the bottom, so the top edge is all cards that have arrived and the bands show where they wait.
- Arrivals = cards created in the period; finished = cards moved into the last list in the period. Work in progress = cards in the lists between the first and the last one, averaged over the days.
- Lead-time estimate by Little’s law: average work in progress ÷ average finished cards per day. It holds for a stable system over the period and is an estimate, not a measured time.

## Limits
- Days are counted in UTC. At most 366 days are drawn.