---
title: "Agent tutorial 2: run the demo app | Speedscale Docs"
description: "Your coding agent clones mock-lab, starts the tutorial app's Postgres with tutorial-db (no Docker), runs the app, and sends it the tutorial traffic once."
canonical: "https://docs.speedscale.com/proxymock/agent-tutorial/run-the-demo-app/"
---

[Documentation index](https://docs.speedscale.com/proxymock/llms.txt) | [Markdown](https://docs.speedscale.com/proxymock/agent-tutorial/run-the-demo-app/index.md) | [Canonical page](https://docs.speedscale.com/proxymock/agent-tutorial/run-the-demo-app/)

# Chapter 2: Run the demo app

Your agent clones mock-lab, starts the app and its database, and checks that the app answers all of the tutorial traffic.

Time: about 1 to 2 minutes.

<a id="prompt"></a>

## Prompt

Pick your language. The prompt is the same except for the directory.

**Go**

```text
Clone https://github.com/speedscale/mock-lab and open tutorial/go. Start its database with tutorial-db as the README describes, run the app, and send it the tutorial traffic once to check it works. Then stop the app and leave the database running.
```

**Java**

```text
Clone https://github.com/speedscale/mock-lab and open tutorial/java. Start its database with tutorial-db as the README describes, run the app, and send it the tutorial traffic once to check it works. Then stop the app and leave the database running.
```

**Python**

```text
Clone https://github.com/speedscale/mock-lab and open tutorial/python. Start its database with tutorial-db as the README describes, run the app, and send it the tutorial traffic once to check it works. Then stop the app and leave the database running.
```

**Node.js**

```text
Clone https://github.com/speedscale/mock-lab and open tutorial/node. Start its database with tutorial-db as the README describes, run the app, and send it the tutorial traffic once to check it works. Then stop the app and leave the database running.
```

<a id="what-the-agent-does"></a>

## What the agent does

This chapter uses no skill. The agent reads the app's README and follows it:

*   Clones mock-lab and reads `tutorial/README.md` and `tutorial/<language>/README.md`.
*   Starts `tutorial-db` in the background from `tutorial/`: `go -C db run .` when Go is installed, otherwise the prebuilt binary for your OS, downloaded once from the mock-lab release. It runs a real Postgres 16 as an ordinary process, with no Docker, on port 54329 with the schema from `contract/schema.sql`. The first start downloads about 30 MB of Postgres into `tutorial/.tutorial-db/`.
*   Builds and starts the app on port 8080, then runs the language's traffic driver, which sends 135 requests: health checks, catalog lookups, 40 orders with their reads, order lists, and a few bad requests that expect 400, 404 and 422.
*   Stops the app and leaves the database running for the next chapters.

<a id="what-you-should-see"></a>

## What you should see

The agent's summary. Trimmed:

```text
The Go tutorial app works: the traffic script sent 135 requests with 0 unexpected responses. The app is stopped and the database is still running.

- Database: I started it from `tutorial/` with `go -C db run .`, as the README says, but in the background instead of its own terminal. It's Postgres 16 listening on `localhost:54329`, with user, password and database all `tutorial`. Its data and the downloaded Postgres are in `mock-lab/tutorial/.tutorial-db/` ...
- App: `go run .` in `tutorial/go` started on `:8080` using the default `DATABASE_URL`. ...
- Traffic: `go run ./cmd/traffic` ran once.
- Stopped: I ended both the `go run` process and the app binary it started, and port 8080 is free again.

To stop the database later, run `go -C db run . -stop` from `mock-lab/tutorial/`.
```

The line that matters is `sent 135 requests, 0 unexpected`. The traffic driver prints one line for each response with an unexpected status. Afterwards the `orders` table holds 40 rows.

<a id="if-it-goes-wrong"></a>

## If it goes wrong

*   **`port 54329 is in use ... already running`.** A `tutorial-db` from an earlier attempt is still running. Use it, or stop it with `tutorial-db -stop`.
*   **`port 54329 is in use` for another reason.** Start `tutorial-db -port <free port>` and point `DATABASE_URL` at that port. In later chapters, use the same port wherever a command maps to `localhost:54329`.
*   **The first start is slow or fails to download.** It fetches about 30 MB of Postgres binaries from Maven Central once. Check your network or proxy, then start it again.

Manual equivalent

```bash
git clone https://github.com/speedscale/mock-lab
cd mock-lab/tutorial
go -C db run .           # terminal 1: runs until ctrl-c
```

Without Go, download `tutorial-db` once instead, as `tutorial/README.md` shows for each OS, and run `./tutorial-db` (or `.\tutorial-db.exe` on Windows).

Then run the app and, in a second terminal, the traffic driver:

**Go**

```bash
cd go
go run .                 # terminal 1
go run ./cmd/traffic     # terminal 2
```

**Java**

```bash
cd java
./mvnw -q package
java -jar target/tutorial-orders.jar                                 # terminal 1
./mvnw -q compile exec:java -Dexec.args="http://localhost:8080"      # terminal 2
```

**Python**

```bash
cd python
python3 -m venv .venv
.venv/bin/pip install -r requirements-dev.txt
source .venv/bin/activate
python app.py            # terminal 1
python traffic.py        # terminal 2
```

**Node.js**

```bash
cd node
npm ci
node server.js           # terminal 1
node traffic.mjs         # terminal 2
```

Stop the app with ctrl-c and leave the database running.

<a id="next"></a>

## Next

[Chapter 3: Record traffic](https://docs.speedscale.com/proxymock/agent-tutorial/record-traffic/)