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# The AI Agent block

The **AI Agent** block is an AI assistant that can automate tasks in Postman Flows. There are two AI Agent blocks: AI Agent Legacy and AI Agent with MCP Server support. The **AI Agent Legacy** block responds to natural language prompts by analyzing data, generating content, making decisions, and calling other flows. The **AI Agent with MCP Server support** block does the same, but instead of calling other flows, it invokes tools exposed by MCP Servers.

The **AI Agent** blocks use one of several AI models to interpret prompts and act on available context. You can pass data to the block as variables in the **Context** section, and each variable's *label* helps the block understand the variable's purpose. The **AI Agent Legacy** block can also use other flows as *tools* to complete its tasks. The **AI Agent with MCP Server support** block can use MCP Servers to build agents that can complete autonomous tasks.

For example, you could give the **AI Agent Legacy** block a list of API endpoints as a variable named **endpoints\_list**. Then, you could select a flow from the **Tools** section that sends a GET request to a provided endpoint. When you prompt the **AI Agent Legacy** block to “Get the content headers for each endpoint in endpoints\_list,” it automatically runs the tool for each one and outputs the results.
Or you could give the **AI Agent with MCP Server support** block a Slack channel ID and add a Slack MCP Server to create an agent that sends updates to the Slack channel with the ID you provided.

## Input

**Context** -  Variables you can reference in your prompt using plain text. The variable's name is called a *label* here because the AI Agent block interprets context about the variable’s value from the its label. For example, an **endpoints** label provides more context than a label like **variable-1**. Click ![Add icon](https://assets.postman.com/postman-docs/aether-icons/action-add-stroke.svg#icon) **Add data blocks** to add more variables. You can add variables to the **Context** section using any of the following data blocks:

* [**String**](/flows/reference/blocks/string/)
* [**Bool**](/flows/reference/blocks/bool/)
* [**Number**](/flows/reference/blocks/number/)
* [**Select**](/flows/reference/blocks/select/)
* [**Get Variable**](/flows/reference/blocks/get-variable/)
* [**Get Configuration**](/flows/reference/blocks/get-configuration/)

## Outputs

**Result** - Sends the result of the AI Agent block's task.

**Evals** - Sends structured eval results when you turn on quality evals or add custom evals. See [Evals](#evals).

## Setup

**Model** - Select the AI model from the dropdown list that best suits your task. Different models consume different amounts of credits. See [Manage your team's Postman Flows credit usage](/docs/billing/flows-usage/#how-flows-consume-credits) for details about how the AI Agent block consumes credits.

**Prompt** - The *system prompt* for the AI agent. A system prompt is static and persists for the duration of the task. Enter a prompt in natural language that describes what you want your agent to do. You can reference variables in the prompt by including the variables' labels as plain text. If you added tools to the block, the AI Agent block automatically uses them if needed to act on the prompt.

**Tools** - Tools are flows your **AI Agent Legacy** block can run automatically. The **AI Agent Legacy** block tries to generate any input data it needs from its own knowledge or from variables you've provided. To use a flow as a tool, the flow must have at least one [snapshot](/flows/build-flows/configure/snapshots/).

To add a tool, do the following:

1. Click the **AI Agent Legacy** block.

2. Click **Add a tool**.

3. Select a tool from the dropdown list.

To select a different snapshot of a tool, do the following:

1. Hover over the tool.

2. Click ![Versions icon](https://assets.postman.com/postman-docs/aether-icons/descriptive-versions-stroke.svg#icon).

3. Select a snapshot from the dropdown list.

When a tool uses [inputs](/flows/build-flows/configure/scenarios/), the **AI Agent Legacy** block automatically populates those inputs with AI-generated data. You can also assign static values to the inputs with a [*configuration*](/flows/build-flows/configure/configure-values-actions/).

> **Note**
>
> Postman Flows doesn't pass static configuration data to the LLM to preserve the security of any secrets.

To select a configuration for a tool, do the following:

1. Hover over a tool.

2. Click ![Setting icon](https://assets.postman.com/postman-docs/aether-icons/descriptive-setting-stroke.svg#icon) **Edit Tool**.

3. Next to the input, click ![Magic icon](https://assets.postman.com/postman-docs/aether-icons/descriptive-magic-stroke.svg#icon) **AI-generated**.

4. Select a configuration from the dropdown list or click ![Open web icon](https://assets.postman.com/postman-docs/aether-icons/action-openWeb-stroke.svg#icon) **Add configuration** to create a new one.

**MCP Servers** - MCP Servers expose specific functionalities that the **AI Agent with MCP Server support** block can use to create agents to automate tasks. There are two types of MCP Servers available: [flows that have been deployed as MCP Servers](/flows/build-flows/ai/mcp-server-flows/create-mcp-server-flow/), and external MCP Servers.

> **Info**
>
> Adding external MCP Servers consumes credits for each unique external MCP Server that your AI Agent calls. If you call the same external MCP Server multiple times, it only consumes credits once for that unique server. Adding Postman Flows deployed as MCP Servers does not consume any credits. To learn more see, [Manage your team's Postman Flows credit usage](/docs/billing/flows-usage/).

To add an MCP Server, do the following:

1. Click the **AI Agent with MCP Server support** block.

2. Click **Add MCP flow** if you have any flows in your workspace that have been deployed as MCP Servers. A list of available flows deployed as MCP Servers appears in the dropdown.

3. Click **Add server** to add an external MCP Server and enter a name and URL for your MCP Server.
   * (Optional) Enter a bearer token if your MCP Server requires one. When you enter a bearer token, Postman Flows saves it as a secret value in a new [configuration](/flows/build-flows/configure/configure-values-actions/). The next time you add an MCP Server, you can choose to reuse that secret bearer token or create a new one.

4. Click **Add** to add the MCP Server.

**Additional Settings** - Appears when you click the block, and enables you to select an AI model or enforce an output schema that you can parse later in the flow.

To enforce an output schema, do the following:

1. Click the AI Agent block, then click ![Setting icon](https://assets.postman.com/postman-docs/aether-icons/descriptive-setting-stroke.svg#icon) **Additional Settings**.

2. Click ![JSON icon](https://assets.postman.com/postman-docs/aether-icons/descriptive-json-stroke.svg#icon) **Enforce output schema > ![JSON icon](https://assets.postman.com/postman-docs/aether-icons/descriptive-json-stroke.svg#icon) Schema**.

3. Click **Generate from example** and paste valid JSON data into the text box, then click **Generate schema**. Alternatively, click **Define custom schema** to manually enter a JSON schema.

**Evals** - Click ![Add icon](https://assets.postman.com/postman-docs/aether-icons/action-add-stroke.svg#icon) **Evals** on the block to grade its output with [evals](/flows/build-flows/ai/evals/), which use an AI model as a judge. Turn on any of the built-in evals under **Quality presets** (**Friendliness**, **Safety**, **Non-toxicity**, **Correctness**, **Relevance**), or add your own under **Custom**. See [Evals](#evals) for details, or [Add evals to a flow](/flows/build-flows/ai/add-evals-to-a-flow/#grade-output-on-the-ai-agent-block) for step-by-step instructions.

## Evals

Evals are opt-in and don't run unless you configure them. Each enabled eval is a separate judge call that consumes Flows credits.

* **Quality presets** grade the output for **Friendliness**, **Safety**, **Non-toxicity**, **Correctness**, and **Relevance**. Turn on each eval you want to run.
* **Custom** evals grade the output against a criterion you write in natural language. Give each custom eval a name and a criterion of up to 4,000 characters. You can add up to 50 custom evals, and the five quality presets don't count toward this limit.

The passing threshold is fixed at 80 on a 0–100 scale, and the judge model is fixed at `gpt-4o-mini-2024-07-18`. The block automatically gives the judge the agent's prompt and inputs as context, which can give criteria such as **Correctness** and **Relevance** enough grounding to produce a score. This also means a check here can score differently from a similar [`pm.eval`](/flows/reference/blocks/evaluate/#define-evals-with-pmeval) check on the **Evaluate** block, which receives only the context you pass to it and defaults to a different judge model.

Before a run, the block shows `No eval results yet. Run the flow to grade this response.` After a run, a preview shows a summary, such as `Passed 3/4`, with a row for each eval and its score. A failed eval was graded but didn't meet its passing threshold. A skipped eval means the judge lacked the information to grade the output, and it's left out of the summary counts.

Evals run when the flow runs, on the canvas, in local mode, and in deployed and scheduled flows. They aren't supported by the [Postman CLI](/docs/postman-cli/postman-cli-flows/). Eval failures don't fail the flow, and the run still completes if grading can't complete. When grading fails, the block shows `Grading failed`, and the **All evals** tab in the run log marks the block as `Grading failed` with no evals graded. Results also appear through the **Evals** output port and in the **All evals** tab of the [run log](/flows/build-flows/troubleshoot/troubleshoot/#run-logs). For details, see [Evaluate AI output with evals](/flows/build-flows/ai/evals/), [Add evals to a flow](/flows/build-flows/ai/add-evals-to-a-flow/), and [Manage your team's Postman Flows credit usage](/docs/billing/flows-usage/).

## Related blocks

* [**AI Request**](/flows/reference/blocks/ai-request/)
* [**Bool**](/flows/reference/blocks/bool/)
* [**Create with AI**](/flows/reference/blocks/create-with-ai/)
* [**Get Configuration**](/flows/reference/blocks/get-configuration/)
* [**Get Variable**](/flows/reference/blocks/get-variable/)
* [**Number**](/flows/reference/blocks/number/)
* [**Select**](/flows/reference/blocks/select/)
* [**String**](/flows/reference/blocks/string/)

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