API, an abbreviation of application program interface, is a set of routines, protocols, and tools for building software applications.

This instructable will explain how to create simple API with PHP.

Requirements

Basic knowledge of PHP and Database.
Simple logics (if,switch)
server/localhost
IDE/Text Editor

Step 1: Server/localhost & Client

its better to use localhost like xampp,mampp,wampp or direct install of apache and mysql

I am using xampp on Ubuntu 14.

Start apache and mysql from manage servers tab.
Create project folder in your htdocs or or apache /var/www/html
windows users it will be in your apache or xampp installation folder .(commonly in C:)

IDE

Any text editor or IDE like Aptana Studio,Dreamweaver,Sublime,notepad++.

Step 2: Coding

In php everything execute in server side and echoed or printed output will be displayed as text.

Header information is very important, else client will not understand how to process the info.

we will be giving output as JSON .

JSON (JavaScript Object Notation) is a lightweight data-interchange format. It is easy for humans to read and write. It is easy for machines to parse and generate. It is based on a subset of the JavaScript.

API must accept incoming request from any type of client . Some API's are only configured as accept certain device or only web browsers.

header('Access-Control-Allow-Origin: *'); // for accepting any origin like localhost ,other.

header('Content-Type: application/json'); //setting header as JSON

Then processing given information.

Getting parameters from POST/GET type.
Switching case or if conditions depend on input.
Storing / retrieving Data from DB or FILE
Display the output.

Step 3: Process Info

For example

http://yourdomain.com/api.php

passing action and info via GET method.

http://yourdomain.com/api.php?action=time

so defined action is time , code will be

$action = $_GET['action'];

switching the action

switch($action){
case "time":
//action code
break;
}

Step 4: Output

Printing output as JSON

echo json_encode(array("title"=>data));

so total code will be

<?php
header('Access-Control-Allow-Origin: *'); // for accepting any origin like localhost ,other.header('Content-Type: application/json'); //setting header as JSON
$action = $_GET['action'];
switch($action){
 case "time": 
 $data=time(); //inbuilt time function in php returns UNIX timestamp
 break;
case "store":
//Store another input in db or file
break;
}
echo json_encode(array("result"=>$data));
?>

so when you call

yourdomain.com/api.php?action=time

result will be

{"result":"1440237956"}