Testing
A sandbox answers every endpoint from fixed data, so you can build and test a client without a key and without touching production.
Setup
The key is public, so it can live in a checked-in test setup.
export ZELF_BASE_URL=https://sandbox-api.hellozelf.comexport ZELF_API_KEY=sk_zelf_sandbox_democurl -H "x-api-key: sk_zelf_sandbox_demo" "https://sandbox-api.hellozelf.com/api/v1/content/?page_size=3"Coverage
It returns the shapes, status codes, error codes and pagination that production returns, and page and page_size work. Every other query parameter is accepted and ignored, so a list returns the same rows whatever you filter on, nothing is validated, and writes persist nothing. That is enough to exercise request building, serialization, paging, authentication and retries.
Anything that depends on a real filter, a real id or a real result has to be checked against production with your own key.