In this guide 6 sections
An API is a set of agreed requests one system can send to another. It lets billing, stock, a website and a CRM share data without anyone retyping it. Each system exposes only what it allows, and the connection is checked and logged. APIs work best when the data rules are agreed first.
What an API does in plain terms
Think of it as a set of agreed requests between two software systems. One system asks, and the other answers. The asking system does not need to know how the other is built.
A useful picture is the counter at a bank. You hand over a slip and get a response, and you never enter the vault where the money is kept.
Most business software offers an API, though what it allows varies a good deal from one product to the next. Accounting tools, payment services, courier platforms and messaging services all do.
One order across four systems
Take an order placed on a website. The website sends the order to the stock system to check availability. The stock system confirms and reserves the items. The billing system raises an invoice. The CRM updates the customer record.
Without APIs, someone copies each step by hand from one screen to the next. With them, each system sends and receives the data it needs on its own. Staff see one record in each place and the same figures.
The courier or WhatsApp update at the end is another API call. It follows the same pattern as every step before it in the chain, and it can be added later without changing the rest.
- Website to stock: is it available?
- Stock to billing: what was reserved?
- Billing to CRM: what was invoiced?
- Order to courier: where should it go?
What has to be agreed before connecting
Technical access is the easy part, and most teams finish it within a short working session once the keys are issued. The harder part is agreement on meaning. Does the website’s customer match the accounting software’s party? Which one owns the address? What happens when the two disagree?
Decide the master for each item, meaning the one system whose record wins. Products may be mastered in stock, customers in the CRM and prices in billing. Other systems then read these but do not overwrite them.
Also decide how often data moves. Some items need an instant update, such as stock levels. Others can move at night.
- Which system owns each type of data
- How a customer or product is matched across systems
- Whether updates are instant or scheduled
- Who is told when a transfer fails
Security, limits and failures
An API call carries business data, so it must be protected. Each connection should use its own key with only the access it needs. Keys should be kept out of code and rotated when staff change.
Services also limit how many requests they accept. A bulk import can hit that limit. The integration should queue work and retry rather than lose records.
Failures will happen, so plan for them. A courier service may be down for an hour. The integration should hold the order, try again after a short wait, and alert a named person if the second attempt also fails.
Where to start
Do not connect everything at once. Pick the one handover that costs most in retyping, such as website orders into billing. Connect it, watch it for a few weeks and then add the next.
Check the API first. Each system you own or buy should have one before you choose it. Some low-cost tools do not. That fact can shape a purchase.
GullySystem’s API and system integration work maps these handovers first, then builds and monitors each connection.
Integration handover map
A one-page map listing each system as a box and each handover as a line. For every line, note the data sent, the owning system, the timing and the person alerted on failure. Use it to plan the first connection and to review later ones.
Open a blank worksheet to printQuestions owners ask
Do all business software tools have an API?
Most current ones do, but the range of what they allow differs. Some offer read access only. Check the documentation before you choose or connect a tool.
Is an API the same as a webhook?
They are related. An API answers when asked. A webhook sends a message when something happens. Many integrations use both.
Are APIs safe for business data?
They can be, when each connection has limited access, keys are protected and activity is logged. Safety depends on how the connection is built and kept.
What if one system has no API?
Options include a file export on a schedule or a tool that reads the screen. These are slower and more fragile, so a different tool may be worth considering.