Xero has the best-documented API of the three and it stopped being free in March.

What the Xero API does and does not allow

The accounting ledger most Australian small businesses run on, and the system every other integration eventually has to agree with.

Everything in the strip above is Xero’s own published documentation, fetched 1 September 2026 and linked to the page it came from. We have not paraphrased it into something friendlier, because the exact wording is what you need when a limit bites at four in the afternoon.

What follows is what those facts mean for a build — the constraints that change a design decision rather than the ones that are merely true. If you want the same treatment for the other eight systems side by side, that is the capability register. If you want to know whether we have built against both sides of a particular pairing, the integration checker answers that specific question.

Bills in: from a supplier PDF to an approved bill

This is the most common thing anyone wants automated in Xero and the most misunderstood. The hard part is not the API call — creating a draft bill is a single POST. The hard part is everything before it: reading a supplier invoice that arrived as a photograph of a printout, deciding which supplier it is when the trading name on the paper does not match the contact record, and working out which job it belongs to.

What the API gives you is a clean boundary to stop at. A bill can be created as a draft, sit there for a human to glance at, and be approved by a person or by a rule. We build almost every accounts payable flow to stop at draft by default, because the failure mode of an over-eager automation in a ledger is not an error message — it is a number that is quietly wrong for a month.

Attachments matter here and have their own limits: ten per document, ten megabytes each, and filenames containing certain characters are rejected outright as a bad request. That last one has broken more supplier-invoice pipelines than any rate limit, because scanner software loves putting colons in filenames.

• Stop at draft The default. A human sees the bill before it hits the ledger, and the automation has done the typing rather than the deciding.
• Approve on a rule Under an amount, from a known supplier, matched to an open purchase order. Three conditions, all auditable, all yours to change.
• Never delete an approved bill Xero will not let you anyway — approved documents are voided, not deleted. Design the reversal path before you need it.

Invoices out: from a finished job to a paid one

The direction that actually moves money. A job marked complete in the field becomes a draft invoice in Xero with the right contact, the right line items and the right tracking categories, and it does so the same day rather than at the end of the month.

Two constraints shape the design. Any line item can carry a maximum of two tracking categories, so if your reporting depends on three dimensions the third has to live somewhere else. And discounts are supported on sales invoices and quotes but not on bills or credit notes, which is a small asymmetry that becomes a large one if you built the credit-note flow second and assumed symmetry.

The bigger point is the one we make on quote to invoice: late payment is the customer’s fault, late invoicing is yours, and it is usually the larger of the two. Xero’s own research puts Australian small businesses at an average of 6.6 days late on payment. A job finished on the third and invoiced on the thirtieth has lost twenty-seven days before anyone was late at all.

Rate limits and what breaks at scale

Xero publishes four limits and they interact in a way worth understanding before you design anything: five concurrent calls, sixty a minute, five thousand a day per organisation, and ten thousand a minute across every organisation your app touches. The concurrency limit is the one people hit first, because it is the one that does not care how patient you are.

The daily limit is the one that changed. Since March 2026, an app on the free Starter tier gets 1,000 calls a day, not 5,000 — and Xero’s own FAQ page still says 5,000 flat, so there are two official pages that disagree. We have linked the tiered one, because it is the newer and the more specific of the two.

What breaks at scale is almost never the limit itself. It is the initial sync. Pulling two years of history for a business with 8,000 invoices, at 100 per page and 60 requests a minute, is a job you schedule rather than a job you run — and it is exactly the shape of work that now also consumes a metered egress allowance.

What Xero does not publish

One of the thirteen fields we track is simply absent from Xero’s documentation: where your client’s data physically sits.

This is the part of an integration page that competitors leave out, and it is the part that costs money. An undocumented rate limit is not an academic gap — it means the first time you find the ceiling is in production, on someone else’s business, usually on the busiest day of their month.

We are not going to fill these in with figures from a forum thread. Numbers circulate for most of them, and some are probably right, but we cannot show you where they came from and neither can the person who posted them. When we have measured Xero properly under load, those figures will appear here with the date we measured them and the conditions we measured them under. Not before.

What we have built, and what we have not measured

We have implemented against Xero in production. That is a real fact and it is also a limited one — it tells you we have solved this system's problems before, and it does not tell you how fast, how reliably, or at what volume.

The honest position is this. Everything on this page above the line is the vendor's published documentation, which we fetched, dated and linked rather than paraphrased. Nothing on this page is a Kindra measurement, because our measured register is not finished and publishing half of it dressed up as all of it would make this page less useful, not more.

What we would do on an engagement is measure the specific things that matter for your build — the endpoints you depend on, at your volume, with your data — and hand you those numbers whether or not they suit us. If they say the integration is harder than we quoted, you get told that too. Start with a Leak Check, or read how we work first if you would rather know the shape of it before talking to anyone.