---
title: Using Tool Variables
slug: guides/agents/tool-variables
---

You can use **tool variables** to specify environment variables available to your custom tools.
For example, if you set a tool variable `PASSWORD` to `banana`, then write a custom function that prints `os.getenv('PASSWORD')` in the tool, the function will print `banana`.

## Assigning tool variables in the ADE

To assign tool variables in the Agent Development Environment (ADE), click on **Env Vars** to open the **Environment Variables** viewer:

<img src="../../images/env_vars_button.png" />

Once in the **Environment Variables** viewer, click **+** to add a new tool variable if one does not exist.

<img src="../../images/tool_variables.png" />

## Assigning tool variables in the API / SDK

You can also assign tool variables on agent creation in the API with the `tool_exec_environment_variables` parameter:
<CodeGroup>
```curl title="curl" {7-9}
curl -X POST http://localhost:8283/v1/agents/ \
     -H "Content-Type: application/json" \
     -d '{
  "memory_blocks": [],
  "llm":"openai/gpt-4o-mini",
  "embedding":"openai/text-embedding-3-small",
  "tool_exec_environment_variables": {
      "COMPOSIO_ENTITY": "banana"
  }
}'
```
```python title="python" {5-7}
agent_state = client.agents.create(
    memory_blocks=[],
    model="openai/gpt-4o-mini",
    embedding="openai/text-embedding-3-small",
    tool_exec_environment_variables={
        "COMPOSIO_ENTITY": "banana"
    }
)
```
```typescript title="node.js" {5-7}
const agentState = await client.agents.create({
    memoryBlocks: [],
    model: "openai/gpt-4o-mini",
    embedding: "openai/text-embedding-3-small",
    toolExecEnvironmentVariables: {
        "COMPOSIO_ENTITY": "banana"
    }
});
```
</CodeGroup>