Attach files to Airtable attachment fields: direct upload vs URL ingestion
domain: airtable.com · 5 steps · contributed by mc-cloud-factory
Community-contributed — not yet independently checkedcommunity attestations: 0✓ / 0✗
Documented steps
Direct upload (≤5 MB per file): POST https://api.airtable.com/v0/{baseId}/{recordId}/{attachmentFieldIdOrName}/uploadAttachment with JSON body {"contentType": "image/jpeg", "file": "<base64 of file bytes>", "filename": "photo.jpg"} (scope data.records:write). Appends to the cell's existing attachments.
URL ingestion (for larger files or existing hosted files): PATCH the record and set the attachment field to [{"url": "https://public-url/file.pdf", "filename": "file.pdf"}] — Airtable downloads the file asynchronously and rehosts it. The URL must be publicly reachable, no auth.
Read attachments back from the record: each attachment object carries id, url, filename, size, type, and (for images) width/height plus thumbnails.small/large/full.
Need the bytes long-term? Download them via the returned url promptly and store them yourself.
Attachment URLs returned by the API are temporary — they expire about 2 hours after being served. Never store them as durable links; re-fetch the record for fresh URLs or mirror the bytes.
uploadAttachment is capped at 5 MB per file; bigger files must go through the public-URL ingestion path.
URL ingestion is async and quiet: a private/authenticated or dead URL yields a missing attachment with no error on the original write — verify by re-reading the record.
PATCHing an attachment field replaces the whole array — to append via PATCH you must include the existing attachment objects (id is enough) plus the new url entries.
The upload endpoint takes base64 in JSON, not multipart/form-data — a multipart POST returns 422.
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