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This document explains how to update a Single Message Transform (SMT) for a
Pub/Sub topic. Changes to SMTs take effect within a few minutes. For
topic SMTs, the changes apply to new messages published after the SMT is updated.
To update topic SMTs, you can use the Google Cloud console, the Google Cloud CLI,
the client library, or the Pub/Sub API.
This predefined role contains
the permissions required to update topic SMTs. To see the exact permissions that are
required, expand the Required permissions section:
Required permissions
The following permissions are required to update topic SMTs:
Grant the update a topic permission on the topic:
projects.topics.patch
Grant the view a topic permission on the project. This permission is only required if you are using the Google Cloud console:
pubsub.topics.view
At the bottom of the Google Cloud console, a
Cloud Shell
session starts and displays a command-line prompt. Cloud Shell is a shell environment
with the Google Cloud CLI
already installed and with values already set for
your current project. It can take a few seconds for the session to initialize.
[[["Easy to understand","easyToUnderstand","thumb-up"],["Solved my problem","solvedMyProblem","thumb-up"],["Other","otherUp","thumb-up"]],[["Hard to understand","hardToUnderstand","thumb-down"],["Incorrect information or sample code","incorrectInformationOrSampleCode","thumb-down"],["Missing the information/samples I need","missingTheInformationSamplesINeed","thumb-down"],["Other","otherDown","thumb-down"]],["Last updated 2025-09-04 UTC."],[],[],null,["# Update topic SMTs\n\nThis document explains how to update a Single Message Transform (SMT) for a\nPub/Sub topic. Changes to SMTs take effect within a few minutes. For\ntopic SMTs, the changes apply to new messages published after the SMT is updated.\n\nTo update topic SMTs, you can use the Google Cloud console, the Google Cloud CLI,\nthe client library, or the Pub/Sub API.\n\nRequired roles and permissions\n------------------------------\n\n\nTo get the permissions that\nyou need to update topic SMTs,\n\nask your administrator to grant you the\n\n\n[Pub/Sub Editor](/iam/docs/roles-permissions/pubsub#pubsub.editor) (`roles/pubsub.editor`)\nIAM role on your project.\n\n\nFor more information about granting roles, see [Manage access to projects, folders, and organizations](/iam/docs/granting-changing-revoking-access).\n\n\nThis predefined role contains\n\nthe permissions required to update topic SMTs. To see the exact permissions that are\nrequired, expand the **Required permissions** section:\n\n\n#### Required permissions\n\nThe following permissions are required to update topic SMTs:\n\n- Grant the update a topic permission on the topic: ` ``projects.topics.patch`\n- Grant the view a topic permission on the project. This permission is only required if you are using the Google Cloud console: ` ``pubsub.topics.view`\n\n\nYou might also be able to get\nthese permissions\nwith [custom roles](/iam/docs/creating-custom-roles) or\nother [predefined roles](/iam/docs/roles-overview#predefined).\n\nYou can configure access control at the project level and at the individual\nresource level.\n\nUpdate topic SMTs\n-----------------\n\nTo update topic SMTs, follow these steps: \n\n### Console\n\n1. In the Google Cloud console, go to the Pub/Sub **Topics** page.\n\n [Go to Topics](https://console.cloud.google.com/cloudpubsub/topic)\n2. Click the topic for which you want to edit SMTs.\n\n3. In the topic details page, click **Edit**.\n\n The **Transforms** tab lists all the SMTs that are attached to the topic.\n4. In the Edit topic page, you can do the following tasks:\n\n 1. Add a new SMT. Click **Add a transform**.\n\n 2. Edit an existing SMT. Expand any SMT to edit the SMT.\n\n 3. Rearrange the SMTs. Use the up and down arrows.\n\n 4. Delete an SMT. Click the delete button.\n\n5. Click **Update**.\n\n### gcloud\n\n1. In the Google Cloud console, activate Cloud Shell.\n\n [Activate Cloud Shell](https://console.cloud.google.com/?cloudshell=true)\n\n\n At the bottom of the Google Cloud console, a\n [Cloud Shell](/shell/docs/how-cloud-shell-works)\n session starts and displays a command-line prompt. Cloud Shell is a shell environment\n with the Google Cloud CLI\n already installed and with values already set for\n your current project. It can take a few seconds for the session to initialize.\n2. Run the\n [`gcloud pubsub topics update`](/sdk/gcloud/reference/pubsub/topics/update)command:\n\n \u003cbr /\u003e\n\n ```bash\n gcloud pubsub topics update TOPIC_ID \\\n --message-transforms-file=TRANSFORMS_FILE\n ```\n\n Replace the following:\n - \u003cvar translate=\"no\"\u003eTOPIC_ID\u003c/var\u003e: The ID or name of the topic you want to update.\n\n -\n \u003cvar translate=\"no\"\u003eTRANSFORMS_FILE\u003c/var\u003e: The path to the YAML or JSON file containing the\n updated SMTs.\n\n The following is an example of a YAML transforms file: \n\n ```yaml\n - javascriptUdf:\n code: \u003e\n function redactSSN(message, metadata) {\n const data = JSON.parse(message.data);\n delete data['ssn'];\n message.data = JSON.stringify(data);\n return message;\n }\n functionName: redactSSN\n - javascriptUdf:\n code: \u003e\n function filterHighAmount(message, metadata) {\n const data = JSON.parse(message.data);\n if (data['amount'] \u003e 100 ) { return null; }\n return message;\n }\n functionName: filterHighAmount\n ```\n\n \u003cbr /\u003e\n\n To clear all the SMTs from the topic, use the following command: \n\n ```bash\n gcloud pubsub topics update TOPIC_ID --clear-message-transforms\n ```\n\n Replace \u003cvar translate=\"no\"\u003eTOPIC_ID\u003c/var\u003e with the ID or name of the topic you want to update.\n\n \u003cbr /\u003e\n\n\u003cbr /\u003e\n\nWhat's next\n-----------\n\n- [Create a topic with SMTs](/pubsub/docs/smts/create-topic-smt)\n\n- [Delete topic SMTs](/pubsub/docs/smts/delete-topic-smt)"]]