493 Unsupported Browser

The HTTP 493 Unsupported Browser status code is an unofficial client error specific to Akamai Enterprise Application Access (EAA), returned when the HTTP request does not contain Server Name Indication (SNI) in the TLS handshake.

Table of Contents

Usage

Akamai EAA returns 493 when the TLS ClientHello message from the client omits the SNI extension. The EAA data POP relies on SNI to route incoming TLS connections to the correct application. Without SNI, the POP has no way to identify which backend the client intends to reach.

Despite the name "Unsupported Browser," the error has nothing to do with browser features or rendering capabilities. The status code targets clients failing to include SNI during the TLS handshake. This affects legacy TLS libraries, older HTTP clients, and automated tools configured without SNI support.

All modern browsers send SNI by default. The error surfaces most often with command-line tools, legacy application clients, or custom integrations using outdated TLS stacks.

SEO impact

Search engines like Google will not index a URL with 493 response status, and consequently, URLs indexed in the past returning this HTTP status code will be removed from search results.

Example

A client connects to an EAA-protected application without sending SNI in the TLS handshake. The data POP rejects the connection.

Request

GET /app HTTP/1.1
Host: app.example.re

Response

HTTP/1.1 493 Unsupported Browser
Content-Type: text/html

<html>
<head><title>Unsupported Browser</title></head>
<body>
<h1>493 Unsupported Browser</h1>
<p>The request does not contain Server Name
Indication (SNI).</p>
</body>
</html>

How to fix

Confirm the client sends SNI during the TLS handshake. Test with openssl s_client:

openssl s_client -connect app.example.re:443 \
  -servername app.example.re

The -servername flag forces SNI inclusion. If the connection succeeds with this flag but fails without, the client's default TLS configuration omits SNI.

Update the TLS library used by the client. Libraries like OpenSSL (versions before 0.9.8f) and older Java runtimes lack SNI support by default. Upgrading to a current TLS stack resolves the issue.

For curl requests, use --resolve or ensure the hostname is passed directly rather than connecting by IP address:

curl https://app.example.re/app

Connecting by IP address bypasses SNI. Always connect using the application's hostname.

Takeaway

The 493 Unsupported Browser status code is an unofficial client error specific to Akamai EAA, triggered by the absence of SNI in the TLS handshake. The name is misleading: the error targets missing SNI, not browser compatibility. All modern browsers include SNI by default. The fix involves updating legacy TLS clients.

See also

Last updated: March 6, 2026