Upload to Backblaze B2

Send every rendered image or PDF to a Backblaze B2 bucket you control.

HTML/CSS to Image connects to Backblaze B2 through its S3-compatible API. A scoped B2 application key supplies the access key ID and secret used by HCTI.

You need:

• An existing B2 bucket.
• The bucket’s B2 region, such as us-west-004.
• An optional key prefix, such as hcti-renders.

The region appears in the bucket’s S3 endpoint: https://s3.<region>.backblazeb2.com.

In the Backblaze web console, open Application Keys and create a new application key.

1. Give the key a recognizable name.
2. Restrict it to the destination bucket.
3. Choose Read and Write access if HCTI may need to create later transformations while HCTI Storage is disabled. Write access is enough for base uploads.
4. If offered, restrict the key to the same file-name prefix you will enter in HCTI.
5. Copy the resulting keyID and applicationKey. The application key secret is shown only once.

Do not use the master application key. Backblaze does not support it with the S3-compatible API.

The credentials map to HCTI fields like this:

For least-privilege custom capabilities, writeFiles provides uploads, readFiles supports later transformations, and deleteFiles supports connection-test cleanup. Some S3 integrations also need listAllBucketNames for a bucket-scoped key, although HCTI’s connection test writes directly to the configured bucket.

Open the Storage Destinations dashboard, click Add storage destination, and enter:

Click Test connection, then enable and save the destination after the test succeeds. Copy the destination id for your API requests.

The test writes a small object under <key-prefix>/.hcti/connection-tests/. Cleanup is best-effort, so missing delete access does not make a successful write test fail.

Pass the destination ID as storage_destination_id when you create an image:

curl -X POST https://hcti.io/v1/image \
  -u 'user-id:api-key' \
  -H 'Content-Type: application/json' \
  -d '{
        "url": "https://example.com",
        "storage_destination_id": "your-storage-destination-id"
      }'

Rendering is lazy. With normal HCTI storage enabled, request the returned image URL to render the image and upload the B2 copy. With Disable HCTI Storage selected, send an authenticated PUT request to the returned /v1/store/... URL.

The base object is stored as <key-prefix>/<image-id>.png, or .pdf when the request uses pdf_options. Your B2 bucket settings determine whether that object is private or publicly accessible.

• Authentication fails with a master key — Create a standard application key; the master application key does not work with the S3-compatible API.
• The connection test uses the wrong endpoint — Enter the region embedded in the bucket’s S3 endpoint, including its numeric suffix.
• A bucket-scoped key is rejected — Confirm the key is scoped to the exact bucket. If the error involves listing buckets, enable Allow List All Bucket Names.
• A later transformation fails with HCTI Storage disabled — Add readFiles access.
• Connection-test objects remain — Add the capabilities Backblaze requires for deleting objects, including deleteFiles.

Backblaze documents creating scoped application keys and calling the B2 S3-compatible API.

You can also automate configuration through the Storage destinations API or MCP tools.