Any chat
Paste the guide
The editor copies the guide as a prompt. Paste it into ChatGPT, Claude, Gemini or a local model, describe the flow, and paste the answer back.
From the maker of topo topo draws systems in space. ack draws them in time. →
Sequence diagrams that run on real time.
Links have latency and work takes time, so arrows slant the way networking textbooks draw TCP and packets fly at the right relative speed. See why TLS 1.3 saves a round trip, why N+1 queries hurt, and what a retry really costs.
Failure injection
Click any message. Watch what breaks.
Drop a request and the sender waits out its timeout, backs off and tries again, and everything downstream shifts. Drop one with no timeout and the rest of the flow greys out: it hangs forever. Drop a response and the retry does the work twice, which is how people get charged twice.
Mermaid import
Every Mermaid diagram you have, animated.
Paste a sequenceDiagram. Participants, arrows, notes, activations and loop, alt, opt and par blocks come across, every hop gets a default latency, and it plays. Then give the links their real numbers.
Made for LLMs
Any model can write it, because it is twenty keywords.
ack is a small text format with a short guide at /llms.txt. Ask a model for the OAuth flow in your codebase, paste the reply, and it runs. Coding agents can validate, render and share diagrams over MCP.
For agents
MCP server
Five tools: the guide, validate (errors, timings, round trips), render an animated SVG, make a share link, and convert Mermaid.
claude mcp add ack -- node ack-mcp.mjs
Share
The link is the file
Diagrams are compressed into the URL, dropped messages included, so a link shows exactly the failure you found. Nothing is uploaded.
Examples
Ten flows worth watching.
Each opens in present mode. Play it, step through it, drop a message, then edit a copy.