Invoice Ninja API vs QuickBooks Online API + MCP

Invoice Ninja API

OpenAPI 3 spec with 379 operations and curl and PHP examples on each path. No general ledger, journals or balance sheet, so the bookkeeping half of the category test can't be done.

QuickBooks Online API + MCP

Official MCP server from Intuit with 145 tools and flags to remove write, update or delete tools. Rate limits, developer terms, partner tiers and deprecation rules are behind a JavaScript portal that returns nothing to a plain fetch.

Invoice Ninja API

1. Send X-Requested-With: XMLHttpRequest with X-API-TOKEN on every call
2. Prototype against demo.invoiceninja.com with X-API-TOKEN: TOKEN before asking for real credentials
3. Add ?mark_sent=true to the save to make an invoice live, or ?send_email=true to send it. A plain create is a draft
4. Stay under 1,000 requests a minute per token on the hosted service and 20 a minute on report exports
5. Record a supplier bill as an expense or purchase order. There's no bills resource

QuickBooks Online API + MCP

1. Store the realmId with the tokens. Every URL needs it and the token alone doesn't name the company
2. Persist the new refresh token from every refresh response. The previous one expires 24 hours later
3. Use the query endpoint with MAXRESULTS and STARTPOSITION for reads rather than fetching by id
4. Send a unique requestid query parameter on writes, so a retry returns the first response instead of posting twice
5. On 429, wait for Retry-After before retrying, and don't retry other 4xx errors