How to choose an accounting API

Start with a complete business transaction

Write a short acceptance scenario before comparing APIs: create a customer, post an invoice with the required tax treatment, record a partial payment, and reconcile the remaining balance. Include the awkward cases your product actually handles: credit notes, foreign currencies, attachments or multiple legal entities.

Decide which system owns each record. A reporting application may only need reads; an accounts-receivable product needs write semantics and a recovery path. Score a missing must-have operation as a blocker rather than hiding it inside an average feature score.

Treat company identity as part of the data model

QuickBooks authorization includes a company realm identifier. Xero’s official SDK works with authorized tenants. Store the provider company alongside every external record identifier; do not assume an invoice ID is globally unique. These are distinct authorization contexts, even when one person administers several companies.

Verify operations, fields and exceptions

Build a small coverage matrix for your chosen workflow: resource, read/create/update support, mandatory fields, pagination, deletion behavior and representative test result. For an aggregation layer, verify the particular connector rather than inferring support from the unified resource name. Apideck publishes a Connector API for this investigation.

Keep provider-specific requirements visible. If a normalized invoice model cannot express a required field, evaluate a documented escape hatch or a direct integration before committing to the architecture.

Run a bounded proof of integration

Use a test company and realistic fixtures. Compare the resulting invoice in the provider UI, including amounts, tax and status, rather than accepting a successful HTTP response as the whole test. Then reconnect the account, retry a timed-out request and run a second sync.

Record engineering effort and support work separately from subscription charges. Choose the option that satisfies your critical workflow with an operational burden your team can sustain; there is no universal best accounting API.