Summary
Both aim at better agent handoff than a naked PNG. Pick SlimSnap if you want free Mac structured JSON capture. Pick Casso if you want numbered multi-region annotations, optional auto-paste, and an agent-agnostic clipboard workflow with a simple one-time license.
Side by side
| Dimension | Casso | SlimSnap |
|---|---|---|
| Core model | Numbered regions + notes + prompt.md + images | Mark element + intent → structured JSON + frames |
| Multi-region feedback | Natural: [1], [2], [3] on one composite | Strong for precise single-element marks |
| Price | 7-day free trial / $29 one-time | Free (Mac) |
| Windows | Same license; Windows app shipping | Mac-first; Windows in progress per their docs |
| Cloud / LLM | No upload; no LLM inside Casso | Local-oriented capture for agent handoff |
Choose Casso when
- You often mark several related UI regions in one pass.
- You want auto-paste into a CLI agent and a consistent prompt format.
- You want one paid tool that covers Mac and Windows under one license.
Choose SlimSnap when
- You want a free Mac-only tool optimized for structured element export.
- Your flow is atomic one-element fixes with JSON for the agent.
FAQ
Related
Try Casso free for 7 days
Numbered screen annotations for Claude Code, Codex, and other agents. 7-day free trial, then $29 once - not a subscription.