The Light API is organised around REST and uses standard HTTP response codes, authentication and verbs. Most endpoints accept and return JSON-encoded data in camel case.
All requests go to:
https://api.light.inc
Where to start
- For the accounting concepts behind the API, Concepts is five short pages on what the API's objects are and why its rules exist. The reference assumes them.
- To start calling the API, Authentication gets you a key, Pagination, filtering and errors covers the mechanics every endpoint shares, and Choosing an endpoint maps common jobs to the calls that do them.
- To connect an AI assistant rather than write code, see Using Light from an AI client.
Enum values and forward compatibility
Some fields in this API use enumerated (enum) values to represent specific states or types. While these enums are fully documented, they are not guaranteed to be exhaustive. New enum values may be introduced over time as the system evolves.
To maintain forward compatibility:
- Always handle unexpected or unknown enum values gracefully.
- Avoid assuming the list of values is complete or immutable.
- Where possible, use string-based comparisons or a safe fallback rather than exhaustive matching.
This policy allows Light to extend functionality without introducing breaking changes for consumers who implement robust handling.
Amounts
Amounts are integers in minor units: 1250 USD is 12.50 USD and 150 JPY is 150 JPY. Each amount is paired with its currency in the same object. Direction (debit or credit) travels separately from size; Reading amounts explains the conventions and the one place their polarity flips.
What should a finance integration pilot prove?
Before writing the connector, name the owner of customers, vendors, contracts, invoices and payment status in each system. Agree the identifiers and direction of updates, then test a correction as well as a successful transfer.
- Permissions: choose the credential and role using Authentication. Test the actions the integration must refuse as well as those it needs.
- Record lifecycle: follow Document lifecycle to separate creating a draft, posting it and recording payment.
- Retries and duplicates: follow Idempotency and each endpoint's notes before retrying a write. Bill creation and four bill actions accept a key, but not every operation does. Test recovery from a timeout without creating a second transaction.
- Completeness and errors: use Pagination, filtering and errors to check a full extract and retain a recoverable error queue.
- Ownership: assign a person to failed transfers, credential rotation, mapping changes and reconciliation of totals back to the source.
Use Choosing an endpoint to check supported operations and documented boundaries. The order to cash guide puts those checks into a CRM, billing and accounting workflow.