Execution Modes

Every function runs in one of three execution modes:

• webhook
• proxy
• isolated

Each mode is useful, but they fit different jobs.

Quick decision guide

• choose webhook when you already have a backend endpoint
• choose proxy when you want to wrap an upstream API as a tool
• choose isolated when you need lightweight custom code in a bounded runtime

Webhook

Webhook mode is the best starting point for most teams.

Use it when you already have an API route or internal service and want Everstack to call it as a tool.

Best for

• customer lookup
• order history
• ticket creation
• account actions
• approval workflows
• internal service calls

Why teams like it

• easy to connect to existing systems
• keeps business logic in your backend
• easiest mode to understand operationally

When not to use it

Do not use webhook mode if the main thing you need is inline custom code and you do not already have a service to call.

Proxy

Proxy mode is for wrapping an upstream API behind a cleaner function interface.

Use it when you want Everstack to front an API and map input or output fields rather than building a custom webhook adapter yourself.

Best for

• simplifying noisy third-party APIs
• exposing only part of an upstream API surface
• normalizing request and response shapes
• building reusable integration wrappers

Why teams like it

• reduces custom glue code
• gives a cleaner tool contract to agents
• useful for platform-style integration layers

When not to use it

Do not use proxy mode if a simple webhook to your backend is easier or if you need arbitrary custom logic instead of request mapping.

Isolated

Isolated mode runs custom code in a bounded isolated runtime.

Use it when you need a small execution unit for transformations, calculations, validation, or integration glue logic.

Best for

• tax calculation
• field normalization
• payload validation
• lightweight enrichment
• format conversion
• custom scoring or routing logic

Why teams like it

• no separate service required
• narrower than a full sandbox
• good for repeatable utility logic

When not to use it

Do not use isolated functions when you really need a live environment with shell access, files, port exposure, or long-running processes. That is a sandbox use case.

Comparison table

Recommended default

If you are unsure where to start, start with webhook.

It is usually the fastest path to production value because most teams already have business logic living in a service they can call.

Related guidance

• Read Functions Overview for the product framing.
• Read Examples for concrete patterns.
• Read Functions vs Sandboxes to understand when isolated functions stop being the right tool.