HubSpot Custom Code Workflow

June 26, 2026

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A workflow that extends HubSpot beyond native actions using custom code, private apps, and external APIs to handle automations like bulk associations, AI scoring, and cross-object syncs.

Elena Mahmutaj

How it works

Step 1: Create a private app

Set up the API access layer that powers all custom code actions.

Go to HubSpot → Settings → Integrations → Legacy Apps.
Click Create a legacy app and name it clearly
Copy the access token shown once on creation and store it securely.

Step 2: Configure scopes

Grant only the permissions the code actually needs.

Add scopes based on the use cases:

CRM data: crm.objects.contacts.read/write, crm.objects.companies.read/write
Deals: crm.objects.deals.read/write
Custom objects: crm.objects.custom.read/write

Step 3: Add the custom code action

Add the code block into the workflow.

In any workflow, click + to add an action and search "Custom code".
Link your private app from the dropdown.
Add the token as a secret in the Secrets tab. Never paste tokens directly into code.

Step 4: Define inputs and outputs

Map the data flowing in and out of the code block.

Add the HubSpot properties the code needs to read as inputs.
Declare up to 25 output fields the code will return.
All outputs cast to strings, so flatten arrays or objects before returning.

Step 5: Write the code

Use the base template, then customise per use case.

Use the standard structure: read inputs, run logic, return outputs via callback.
Stick to available packages: axios, lodash, moment (no npm installs).
Keep code under the 20-second timeout and 128 MB memory limit.
Use AI prompts to generate code faster. Fill in inputs, API URL, and auth, then paste output into the editor.

Step 6: Test before activating

Run the action against a real record before going live.

Click Test inside the code action panel.
Pick a record with the required input fields filled in.
Check that output values match what downstream actions expect.

Step 7: Apply to common use cases

Use custom code to solve what native workflows can't.

Bulk associations: auto-associate or dissociate records based on shared field values.
Recurring deal line items: copy line items onto renewal deals when a deal closes won.
ICP scoring: score accounts on enrollment using firmographic logic.
External enrichment: call any external API and write results back to HubSpot.
Slack notifications: fire webhooks when records hit specific states.