GoHighLevel AI Studio: Custom Code, JavaScript & API

GoHighLevel’s AI Studio lets you describe a website or funnel in plain language and watch it build itself. That speed is genuinely useful, but at some point you hit the edge of what point-and-click can do — a real-time quote calculator, a form that pre-fills from the logged contact, or a submission that posts to your own API. That’s where custom code, JavaScript and the GHL API v2 come in.

This guide is for builders who want to extend the gohighlevel ai studio website builder with custom code, javascript and the api — cleanly, securely and in the right place. We’ll show you exactly where code lives, how to grab the identifiers you need, and three real things you can ship this week.

Where custom code lives in GoHighLevel

There isn’t one magic box. GHL gives you several injection points, and choosing the right one matters for both behavior and security.

• The Custom Code / Custom JS-HTML element: Drop this element onto any page or funnel step in the builder and paste raw HTML, CSS and JavaScript. This is the home for widgets — calculators, embedded apps, interactive UI. AI Studio even ships a built-in Code Editor so you can edit the code behind an AI-generated project directly.
• Page / funnel Header & Footer tracking code: Found in the page or funnel settings, these fields inject scripts site-wide or step-wide. Use the header for things that must load early (a font, a config object) and the footer for scripts that should run after the page renders.
• The workflow Custom Code action: This runs server-side JavaScript inside a workflow, not in the browser. You pass values in through an InputData object — mapped from merge fields and previous steps — and run logic safely away from the visitor’s eyes. This is where secret API calls belong.

The AI website builder and its code injection points

The AI website builder (part of AI Studio) generates a working project from a prompt, a URL or a reference design. You don’t lose control once it’s built: the Code Editor exposes the underlying files so you can adjust markup, styles and behavior, and on a standard funnel or website you still have the Custom Code element plus the Header/Footer fields.

A simple mental model: use AI Studio to generate the structure fast, then layer javascript in gohighlevel on top through the element or footer for the interactive parts the AI can’t infer. The ai website builder ghl gives you the skeleton; your code gives it behavior.

Getting identifiers: contact_id and location_id

The moment you want code to talk to GHL data, you need two identifiers, and confusing them is the most common mistake we see.

• contact_id identifies a single contact (a person) inside a sub-account. You use it when reading or updating one record — fetching a contact’s details, adding a tag, updating a custom field.
• location_id identifies the sub-account (the “location”) itself. The API uses it to scope your request to the right account, and almost every v2 endpoint expects it in the path or body.

You expose these to your code through merge fields / custom values. On a page, GHL can render the current contact and location identifiers into the markup; in a workflow Custom Code action, you map them into InputData using the custom value picker. The pair — contact_id location_id — is what lets your script know who it’s acting on and where.

How to read them in front-end code

In a Custom Code element, you typically read a merge field that GHL has rendered into the page (for example, writing the contact id into a hidden input or a small JavaScript config object in the footer), then reference it from your script. Treat anything the browser can see as public — never put a private key next to it.

Calling the GHL API v2 from custom code

GHL’s API v2 is the current standard (v1 reached end-of-support at the end of 2025). It’s a REST API: you make authenticated requests to endpoints for contacts, conversations, calendars, payments and more, and you scope them with the identifiers above.

The critical rule: where you call it from decides everything.

• Server-side (the workflow Custom Code action): Safe to authenticate and call the API here. Your token never reaches the browser. This is the right place to enrich a contact, sync data or trigger an external system.
• Browser-side (the Custom Code element): Anything here is visible to the visitor. Never embed a secret API key, private token or anything that grants account access in front-end code. If a widget needs server data, have it call a small endpoint you control (or a webhook) that holds the secret instead.

The pattern we use repeatedly: the front-end widget collects input and the contact_id, then posts to a Webhook or your own serverless function; that function (with the secret safely stored) calls the GHL API v2 using the location_id to scope the request. Front-end stays dumb and public; secrets stay server-side.

Three real things you can build

1. A custom calculator / quote widget

Drop a Custom Code element onto a funnel step with a few inputs — square footage, headcount, plan tier — and write JavaScript that computes a live price as the user types. It’s pure front-end math, no secrets needed, and it dramatically lifts conversion versus a static price table. Write the final number into a hidden form field so it’s captured on submit.

2. Pre-filling a form from a contact

When a known contact lands on a page (say, from an email link), render their details via merge fields and use a short footer script to populate the form — name, email, current plan. Read the rendered contact_id so the submission updates the right record. Less typing means more completed forms.

3. Posting data to an external API on submit

Attach a submit handler in a Custom Code element that, on form submission, posts the captured data to an external system — your CRM, an inventory tool, a Slack alert. For anything requiring a secret, route it through a workflow Webhook or Custom Code action so the credential lives server-side, not in the visitor’s browser.

FAQ

Can I run server-side code without an external server?

Yes — the workflow Custom Code action runs JavaScript server-side inside GHL, with values passed in through InputData. For heavier or external logic, a webhook to a serverless function gives you more room.

Is it safe to call the GHL API from a Custom Code element on a page?

Only for requests that don’t require a secret. Anything in a page element is public. Keep tokens and private keys in the workflow Custom Code action or a server you control.

Do I always need both contact_id and location_id?

You almost always need location_id to scope a v2 request to the right sub-account. You add contact_id whenever the action targets a specific person.

Will my custom code survive an AI Studio regeneration?

Edits made in the Code Editor persist, but re-prompting the AI to rebuild a section can overwrite it. Keep critical custom logic in clearly separated elements or footer scripts so it’s easy to re-apply.

Ship it without the guesswork

Extending AI Studio is where GHL goes from a fast site builder to a genuine application platform — but the line between front-end and server-side, and the handling of identifiers and secrets, is exactly where most builds break or leak. If you want custom calculators, API integrations or in-page apps built right the first time, our Vibe Coding service is built for this. Contact us and tell us what you’re trying to build — we’ll map the cleanest, safest path to ship it.