0 - 25.php
<!DOCTYPE html><html><style>form,table{text-align:center}html{background:linear-gradient(0deg,#dfd, #dff, #ffd);}*{font-family:sans-serif;margin:0.4em}input{padding:0.4em;background:#ffd;border:2px solid #930;border-radius:8px}body{padding:20%}td{border: 4px solid #aaf;border-collapse:collapse;border-radius:8px}</style>
<body><form action="" method="get"><center><table>
<tr><td>Number:</td><td><input name="c" placeholder="Number/String" value="<?php echo htmlspecialchars($_REQUEST['c']??''); ?>"></td><td><mark>:3</mark></td></tr>
<tr><td>From base:</td><td><input name="f" placeholder="Base (10|36)" value="<?php echo htmlspecialchars($_REQUEST['f']??''); ?>"></td><td><mark>:v</mark></td></tr>
<tr><td>To base:</td><td><input name="t" placeholder="Base (10|36)" value="<?php echo htmlspecialchars($_REQUEST['t']??''); ?>"></td><td><input type="submit" value="Go"></td></tr>
<tr><td>Output</td><td>
<?php
if(!empty($_REQUEST['c'])){
 if($_REQUEST['f']>0 || $_REQUEST['t']>0){echo '<input disabled value="'.base_convert(preg_replace('/[^\da-z0-9]/i', '', strtolower($_REQUEST['c'])),$_REQUEST['f']??10,$_REQUEST['t']??36).'">';}
 else{echo '<input disabled value="'.crc32($_REQUEST['c']).'">';}}
else{echo '<mark>'.(PHP_INT_MAX).'</mark>';}
?></td><td><mark>:D</mark></td></tr></table><p><br><br>I made this to convert numbers between bases 2 and 32. <br>Numbers 2^63 or bigger may be inaccurate. <br>Also, crc32() will be used for base -1</p></center></form></body></html>