Functions Overview

Functions are Everstack's reusable tool layer.

They let you turn APIs, services, and small units of custom logic into named tools that agents and workflows can call when they need to take action.

The important framing is this: functions are not just for running code. They are how you connect AI systems to real business operations.

What a function is

A function is a registered tool with:

• a name
• a description
• a parameter schema
• an execution mode
• controls like timeout, memory, retries, and enabled state

Once registered, a function can be attached to agents, troopers, and workflow nodes.

Why functions exist

Functions solve a very specific problem: an LLM can reason, but it still needs a safe and structured way to do useful work.

Functions provide that structure.

Use them when you want AI to:

• look up customers, orders, or tickets
• trigger backend actions
• call internal tools or external APIs
• run small transforms or calculations
• reuse the same action across many agents and workflows

Where functions fit in Everstack

Functions sit between reasoning and execution.

1. an agent or workflow receives a task
2. the model decides it needs a tool
3. Everstack exposes matching function definitions to the model
4. the selected function runs in its configured mode
5. the result comes back into the agent or workflow

That makes functions the action layer for production AI systems.

Common use cases

Business system lookups

Expose tools like search_customers, get_order_history, or lookup_incident so an assistant can answer questions with live data.

Operational actions

Expose tools like create_jira_ticket, refund_order, page_oncall, or send_approval_request so agents can do real work instead of only generating text.

Lightweight custom logic

Use isolated functions for tax calculation, payload validation, field normalization, scoring, and data shaping.

Shared tool catalogs

Define a function once and reuse it across multiple agents and workflows instead of rebuilding the same integration repeatedly.

Why users value functions

Functions are often one of the most production-useful features in Everstack because they are:

• narrower than a sandbox
• easier to reason about than broad compute access
• highly reusable
• close to existing APIs and services teams already own

In many organizations, functions are configured occasionally but invoked constantly.

Functions and sandboxes

Functions and sandboxes are complementary.

Use functions for repeatable actions with a clear contract. Use sandboxes for shell access, files, long-running processes, or interactive execution.

Read Functions vs Sandboxes for the full decision guide.

Next steps

• Read Execution Modes to choose between webhook, proxy, and isolated execution.
• Read Examples for common function patterns.
• Read Attaching Functions To Agents And Workflows to connect functions to runtime behavior.
• Read Functions vs Sandboxes to decide which primitive fits your use case.
• Use the Functions API to create and manage functions programmatically.