Design diagrams
Diagrams that show what a pull request changes: data flow and sequence.
A diff shows lines; it does not show how the change works. After a review, Limn draws a design diagram of the pull request: what touches the data, across the top, and each step down the page in the order it happens. It is drawn by a separate run, so it never delays the review.
#What you see
Screen API route · changed Service · changed Database
| Step | From → to | What passes |
|---|---|---|
| 1 · call | Screen → API route | refund amount, order id |
| 2 · validate | API route | amount is whole pence and above 0 |
| 3 · read | Service → Database | order.paid_at |
| 4 · write | Service → Database | refund row |
Redraw
The diagram is in the AI Review tab, under Design. It has two to seven lanes, left to right in the order the data first reaches them. Each lane is one kind of thing: Screen, API route, Service, Queue / job, Database, File / cache or Outside API. A lane's border says whether the pull request adds it, changes it, or leaves it as it was.
#Read the diagram
- Steps are numbered in the order they happen, and each arrow names the data that passes.
- A dotted line is a check, a heavy line a write to where data is kept, and a dashed line a result going back.
- The keys under the diagram name the lines and box borders.
- Click a step to open its file in the Changes tab.
- In a ticket's story view, the diagram covers every pull request of the ticket, and each box and step names the pull request that does it.
#Draw or redraw
- Open the pull request's AI Review tab and find Design.
- Press Draw (or Redraw when there is one). The button reads Drawing… while it runs.
A diagram is drawn again after a review of a new commit, unless you turn that off. It is always drawn by a mid-sized model (Sonnet on Claude), whichever model reviewed.
#When there is no diagram
A change with no data path gets none, and Limn says why in one line, for example No diagram: this change only edits copy. This happens when the change edits only text or tests, changes only a few lines, or the model finds it moves no data. Draw asks for one anyway.
#Turn it off
In Settings → AI review, untick Draw a design diagram after each review. Turning it off saves about a third of a provider's review usage. You can still press Draw on any pull request. See Settings → AI review.