Proschi Tested: Claude Code Draws Your App in the Terminal and Plays Every Request

You click Place order. A second later, you get a green tick. In between, your order went through eighteen steps, across eleven different pieces of software, written in five languages. And almost nobody on the team can draw that from memory.

A free plugin called Proschi makes Claude Code draw that picture right inside the terminal, then play each request across it, step by step. We pointed it at a real online shop with the documentation deleted, checked every arrow against the code, and pushed 500 simulated orders a second through it. It found 15 out of 15 official connections, and something broke at load that we didn't expect.

The Reddit post, and what we tested

This week, a developer on r/ClaudeCode, u/gvart, showed Claude Code drawing architecture diagrams in the terminal and playing request flows on them. The top question under the post was: can I just point it at my code, and have it fill in the gaps? The author said he hadn't tested that. So we did.

What Proschi is, and the 2-line install

Proschi is free and open source (MIT license). You describe your system in a few lines of plain text: the boxes, the arrows, and the journeys a request takes. Proschi lays it out, and with its plugin, Claude Code draws it right in your terminal. No browser.

Installing it is two lines inside Claude Code:

• /plugin marketplace add gvart/proschi
• /plugin install proschi@proschi

Besides the drawing, it ships seven skills. A skill is a saved set of instructions Claude can follow on cue. These ones:

• Turn Terraform, Kubernetes or docker-compose files into a diagram
• Rebuild a diagram from a whiteboard photo
• Write the journeys from your code
• Size it for your traffic
• Review a design
• Keep your diagrams in sync with every pull request
• Write the design doc

Before you read on, a guess. Five hundred people press Place order every second. Which part of the shop breaks first? The payment service? The database?

The test: a real shop, docs deleted

We used Google's Online Boutique, a demo shop with eleven services written in Go, C#, Node, Python and Java. We deleted the README and the docs, so Claude only had the code. The official docs went aside as the answer key. Setup: Claude Code with Opus 5.5 and Proschi 0.12.0.

Then we typed one request: map this online shop in Proschi using only the code. Add use cases for Place an order, including a declined card, and Browse a product. Then test it at five hundred orders a second, with ninety-nine percent of orders under five hundred milliseconds, and fix whatever breaks.

The map: 15/15, and can Claude fake it?

About a minute later, Claude wrote the file, and the plugin drew the diagram right under it. Google's official diagram has fifteen connections. Claude found all fifteen.

One comment on the Reddit post asked: can't Claude just fake the diagram? So in a second run, we made it show the exact line of code behind every arrow, and we opened nineteen of those lines ourselves. Nineteen out of nineteen were right.

And when it had to guess, like how many items sit in a typical cart, it wrote the word "assumption" right next to that line. That's what makes a diagram something you can trust.

Fair fight: plain Claude + Mermaid

To be fair, we also ran Claude with no plugin, just plain Mermaid (a common text format for drawing diagrams). It also found all fifteen, in about the same time: 3 minutes 12 seconds, against 3 minutes 36 seconds for the Proschi run. So mapping the shop isn't the magic. Here's what Mermaid alone can't do.

Watch an order travel (and a declined card)

We asked Claude to show how Place an order flows, and the diagram appeared right inside its reply. Press play, and you watch the order move: the front end, the checkout, the shopping cart, a price for each item, the shipping quote, and then the card charge. Eighteen steps in all.

Then the bad day. Switch to the declined card. Same start, but the card bounces at payment, checkout sends back an error, and the shopper gets an error page. The email and the recommendations never run. Ten steps instead of eighteen, and we never left the terminal.

500 orders a second: what broke

This part wasn't in the Reddit post. Proschi can also simulate traffic. We asked for five hundred orders every second, with ninety-nine percent of orders done in under half a second. (That "ninety-nine percent" target is often called p99.)

It wasn't payment, and it wasn't the database. It was the product catalog, at 220 percent of what it could handle. The currency service was also over, at 123 percent.

Here's why. Every order asks the catalog nine times: three times to price the three items in your basket, once for the recommendations, and five more to show those recommended products. So five hundred orders a second becomes about 4,400 requests, on one copy of a service built for about 2,000.

Claude spotted it and fixed it: four copies of the catalog, and two of the currency service. It even put the change into the Kubernetes files, and added a test so it can't quietly slip back. Run it again, and ninety-nine percent of orders finish in 164 milliseconds.

These are modeled numbers, not a real load test, and Claude said so itself. Its last tip was a cheaper fix than more servers: fetch those five recommended products in one call instead of five, and catalog load drops by more than half (Claude's estimate). That's exactly what you want to know before Black Friday, not during it.

The catch: what plain Claude caught

Now the honest part. The plain Mermaid run spotted something the Proschi run missed. In this shop, your card is charged before your order ships. If shipping fails after that, nothing refunds you. You're charged, and you get no order.

So here's our rule. Let Proschi draw it and stress it. Then ask Claude one more question: what can go wrong between these steps?

3 doubts from the comments

• Do you need monitoring or telemetry? No. It read only the code and the deployment files.
• Why not just use a Claude artifact? You can, but an artifact is a picture in your browser. This stays in your terminal, plays every journey, and does the math on your traffic.
• Do the skills cost extra tokens? A little. In our test, the Proschi run cost about the same as the plain one, a dollar and change at API prices.

Your app in 3 prompts

1. Map it. Map my app in Proschi using only the code, and mark every guess. Then open five of the code lines it points to and check them yourself. That's the thirty-second trust check.
2. Add the journeys that matter, like sign up, checkout and search, each with one failure path, and play them.
3. Give it your real traffic, ask it to fix what breaks, and then ask the one question that catches the rest: what can go wrong between these steps?

No plugin? The same skills work in Codex and Cursor. You just won't get the drawing in the terminal.

Get the Flow Card

So, back to that button. Now when you click Place order, you can watch it go: every step, the error path when a card bounces, and the one service that melts at five hundred orders a second. All in the terminal. The install lines, our three prompts and the thirty-second trust check are in one free PDF. Comment FLOW on the video, or grab it below.

How we tested: Claude Code with Opus 5.5, Proschi 0.12.0, Google's Online Boutique demo shop with README and docs removed, October 30, 2026. Load numbers come from Proschi's model with default capacities: a demonstration, not a real load test. Proschi by u/gvart (MIT). One small test, not a study. Independent, not sponsored by or affiliated with Proschi or Anthropic.