Three Ways Into a Tool: An API, a Middleman, or a Login

So every AI product you look at says it integrates with your tools, and that word is doing a lot of work, because there are exactly three ways to get into a piece of software and they are not the same thing. I want to walk through them the way I'd explain it to an owner, not an engineer, because the difference decides what the thing can actually see and what happens when it breaks.

One. The direct API

The tool publishes a doorway for other software, and somebody holds a credential and walks through it. The connection is direct, the data is structured, you can read history, and you can write back. This is the best way in when it exists, and it comes with rules the vendor sets that nobody tells you about.

Take QuickBooks Online, since almost everybody has it. Intuit's own token policy is that the access token lasts an hour and the refresh token that gets you a new one lasts 100 days, and the refresh token itself rotates, so whoever holds the connection has to store the newest one every time or the connection dies. In practice that means a QuickBooks sync somebody set up in the spring can quietly stop working in the summer, and the first anyone knows about it is a report that's a month stale. There are also limits on how many requests you can make in a minute, so pulling three years of history isn't one call, it's a patient process that has to respect the vendor's pace.

So the questions to ask about a direct connection are, who holds the credential, what happens when the token expires, and can you see history or only what happens from today forward.

Two. The middleman

The second way in is you don't connect to the tool at all. You connect to a service that's connected to the tool, and it passes things along. Zapier is the famous one. Something happens in system A, the middleman notices, and it pokes system B.

This is fine for events. A new lead comes in, send a text. An invoice gets paid, post to Slack. What it's bad at is history and identity. It sees the moment, not the record. It usually can't answer what this customer's total for the year is, because it never held the year, it held a series of moments as they went by. And you're paying per moment, so the businesses that need it most, the ones with a lot going on, pay the most for the shallowest view.

We still plug one in when a stack calls for it, for the events. It just isn't where the business lives.

Three. The login

The third way in is the one getting a lot of attention this year. A machine gets its own computer, it signs into the tool with a login the way a person would, and it clicks around.

This is the only way into a tool that has no API, and there are a lot of those. Older field software, the vendor portal that only exists as a website, the county permit system, the supplier that only takes orders through a form. For those, a login is the only door there is.

It's slower than an API, it breaks when the vendor redesigns a page, and it needs a receipt, meaning a record of exactly what it did and saw, because a person can't watch it work. When it has that, it's a real employee at a keyboard. When it doesn't, it's a liability with a password.

The question that actually matters

So those are the three doors. And the thing I'd tell any owner evaluating any of this is that the door isn't the point. What matters is what's on the other side of it. If three tools come in three different doors and land in three different places, you've got three integrations and no picture. If they all land in one place, normalized so that a customer in the CRM and the same customer in the books are one customer, then the door each one came through stops mattering, and you can finally ask a question that spans them.

That's how we built Liaison. We build direct connectors where the API exists, we plug in middleware when a stack calls for it, and when a tool only has a login, Liaison signs in and works it the way a person would. All three lanes land in one lake, every record keeps its source, and every answer traces back to where it came from. We wrote about doing that without migrating anything and about why the agents vendors ship only see their own app, and this is the plumbing under both.

So the next time somebody tells you their product integrates with your tools, ask them which door, who holds the key, and where the data lands. The answers tell you what it can actually do for you.

If you've got a tool with no API that's holding up everything else, tell me which one. That's usually the fun part.