Preview a check
lob_checks_previewIdempotent
Validate a check payload and receive a textual summary. Obtain a confirmation token to commit the same payload when creating the check.
Instructions
Validate a check payload and return a textual summary. Lob does not produce check proofs, so no PDF is rendered. Returns a confirmation_token to pass to lob_checks_create — required in live mode. The token binds the payload: committing a different amount or recipient is rejected.
Input Schema
TableJSON Schema
| Name | Required | Description | Default |
|---|---|---|---|
| description | No | Internal description (max 255 chars). | |
| to | Yes | Recipient address. Either a saved address ID (`adr_…`) or an inline address. | |
| from | Yes | Sender (return) address. Either a saved address ID (`adr_…`) or an inline address. | |
| send_date | No | ISO 8601 timestamp (e.g. '2026-05-01T00:00:00Z') to schedule the send. Must be at most 180 days in the future. | |
| mail_type | No | Mail class. Defaults to usps_first_class for most pieces. | |
| merge_variables | No | Key/value pairs substituted into Handlebars-style {{variables}} in your HTML/template content. | |
| metadata | No | Up to 20 string key/value pairs to attach to the resource. | |
| billing_group_id | No | Billing group ID (`bg_…`) to attribute the charge to. | |
| use_type | No | Required for some mail classes. 'marketing' for promotional, 'operational' for transactional. | |
| bank_account | Yes | Verified Lob bank account ID. | |
| amount | Yes | Check amount in USD (e.g. 125.50). | |
| check_number | No | Optional check number; auto-assigned if omitted. | |
| memo | No | Memo line on the check (max 40 chars). | |
| message | No | Plain-text message printed on the bottom of the check page (max 400 chars). Mutually exclusive with `check_bottom`. | |
| check_bottom | No | Custom artwork for the bottom half of the check page. Accepts a Lob template ID (`tmpl_…`), an HTML string, an https:// URL, or a base64 PDF. Mutually exclusive with `message`. | |
| logo | No | Logo printed on the check face (upper-left, grayscale; PNG or JPG). | |
| attachment | No | Secondary document included in the envelope after the check page. Up to 6 pages. | |
| idempotency_key | No | Idempotency key (max 256 chars). If omitted, the server auto-generates a value derived from the confirmation_token when present, otherwise a fresh UUIDv4. Lob deduplicates identical keys for 24 hours. | |
| extra | No | Additional Lob API parameters not enumerated above. Merged into the request body verbatim. See https://docs.lob.com for the full parameter list per resource. |