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# Simulate real-world conditions in Postman
Postman Simulator is available on Postman Solo, Team, and Enterprise plans. For more information, see the [pricing page](https://www.postman.com/pricing/).
With Postman Simulator, you can create simulations to test how your service behaves under real-world conditions by applying failure scenarios like latency, errors, and rate limits.
Simulations can be applied to [local mock servers](/docs/design-apis/mock-apis/local-mock-servers), which enable you to simulate your API's dependencies and test how your service behaves without calling real services.
Scenarios are applied dynamically as your mock server handles requests. This enables you to observe how your service responds to disruptions and performance constraints. With simulations, you can identify and fix issues before deploying to staging or production.
Postman Simulator is only supported in Local View on the Postman desktop app.
## Create a simulation
Create a simulation to apply failure scenarios to one or more mock servers. Before you create a simulation, make sure you have at least one local mock server set up. To learn how, see [Simulate your API using a Git-backed mock server](/docs/design-apis/mock-apis/local-mock-servers).
To create a simulation, do the following:
1. Open a workspace and select **Tools > 
Simulator** in the footer.
2. Click 
**Create simulation**.
3. Select the mock servers you'd like to add to the simulation. To remove a mock server from the simulation, click 
**Actions** and select **Remove mock**.
4. Turn on the toggle next to the scenarios you want to simulate for each mock server:
* **Simulate Error Responses** - Simulate error responses by returning a specified HTTP status code.
* **Add Response Delay** - Simulate network latency by adding a delay (in milliseconds) before the mock server sends a response.
* **Simulate Rate Limiting** - Simulate rate limiting by specifying a maximum number of requests allowed per minute.
* **Chaos Mode** - Randomly fails a percentage of requests with 5xx status codes.
If you enable both **Simulate Error Responses** and **Chaos Mode**, and the configured error response is a 5xx status code (such as `502`), Chaos Mode only returns that specific 5xx error. For example, if you select `502`, Chaos Mode only returns `502` responses.
If your goal is to test 5xx failures, use either **Simulate Error Responses** or **Chaos Mode**.
5. [Start a simulation](#start-a-simulation) and send requests to the mock server URL.
A [simulation file](#about-the-simulation-file) is created in your local Git repository with the configuration for the simulation.
### About the simulation file
When you create a simulation, Postman creates a simulation file in your local Git repository with the configuration for the simulation, including the mock servers and scenarios. This file is used to start the mock servers with the selected scenarios when you start a simulation.
The simulation file is located at `postman/simulations/.sim.yaml`. You can edit this file directly to update the mock servers and scenarios included in the simulation. You can also use Agent Mode to quickly update the simulation file.
## Start a simulation
You can start all mock servers in the simulation or start them individually. You can also start a simulation using the Collection Runner or the Postman CLI.
To start a simulation from Postman Simulator, do the following:
1. Open a workspace and select **Tools > Simulator** in the footer.
2. Click the simulation you'd like to start.
3. (Optional) Update the mock servers and scenarios in the simulation.
4. Click **Start all** to start all mock servers in the simulation, or click 
**Start mock server** to start an individual mock server.
5. Send requests to the mock server URLs and observe the responses with the simulated conditions applied.
To start a simulation with the Collection Runner, see [Run a collection with a simulation](/docs/collections/running-collections/run-collection-with-simulation).
To start a simulation with the Postman CLI:
* Use the `postman simulate run` command to start a simulation. See [Simulator commands](/docs/postman-cli/postman-cli-simulator#postman-simulate-run) for details.
* Use the `--simulate` option with the `postman collection run` command to run a collection with a simulation. See [Collection commands](/docs/postman-cli/postman-cli-collections#postman-collection-run) for details.
## Update a simulation
To update a simulation, do the following:
1. Open a workspace and select **Tools > Simulator** in the footer.
2. Click the simulation or select **Actions > Open** next to a simulation.
3. Update the mock servers and scenarios included in the simulation.
You can also click **Actions** next to a simulation to duplicate or delete it.