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How to upload images to help center articles using the API

Upload the file with createWorkspaceFileUploadUrl, then reference it in the article's contentHtml with the data-workspace-file-id attribute. Plain fills in the src URL.

  1. Call createWorkspaceFileUploadUrl with visibility: PUBLIC. The mutation returns a workspaceFileId, a presigned uploadFormUrl and a set of uploadFormFields.
  2. Make a multipart POST to the uploadFormUrl. Add all returned uploadFormFields as form fields first, then your file as the file field last. A successful upload returns HTTP 204.
  3. In your upsertHelpCenterArticle call, add an <img> tag to contentHtml with data-workspace-file-id instead of src.
<img data-workspace-file-id="wf_01ABC123" alt="Description of image" />

When the article is saved, Plain moves the file to public storage. Once published, the image is served from a stable public URL that does not expire.

Why createWorkspaceFileDownloadUrl returns a 403

You do not need createWorkspaceFileDownloadUrl. It returns a signed URL for the file while it is still pending. A file only becomes public once an article references it with data-workspace-file-id, so using the download URL as an img src will always return a 403.

Limits

  • Maximum file size: 50 MB
  • Supported formats: JPEG, PNG, GIF, WebP, SVG

Self-hosted images

You can also use standard <img src="https://..."> tags in contentHtml to host images yourself. Plain does not restrict or proxy external image URLs, and no content security policy blocks them in the published help center.

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