> For the complete documentation index, see [llms.txt](https://developer.celigo.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://developer.celigo.com/api/api-reference/scripts-and-stacks.md).

# Scripts & stacks

Custom code and where it runs. Scripts are JavaScript hooks invoked at defined points in flows, exports, imports, APIs, and tools. Stacks point at your own server or AWS Lambda runtime when that code should execute outside Celigo's hosted JavaScript runtime.

| Resource                                                                             | What it covers                                                                            |
| ------------------------------------------------------------------------------------ | ----------------------------------------------------------------------------------------- |
| [Scripts](https://developer.celigo.com/api/api-reference/scripts-and-stacks/scripts) | JavaScript hooks such as preSavePage, preMap, postMap, postSubmit, filter, and transform. |
| [Stacks](https://developer.celigo.com/api/api-reference/scripts-and-stacks/stacks)   | Your own server or AWS Lambda runtime for executing extension code.                       |