It was primarily designed for the Java ME platform, as a low-end sibling for Opera Mobile, but as of January 2025[update] only the Android build was still under active development.

[13] Opera Mini was originally intended for use on mobile phones not capable of running a conventional Web browser.

[19] On 1 November 2006, Opera Mini 3 beta introduced secure browsing, RSS feeds, photo uploading and content folding.

According to Johan Schön, technical lead of Opera Mini development, the entire code had been rewritten.

[24] Using a built-in pointer, the user can zoom into a portion of the page to provide a clearer view; this is similar to the functionality of Opera's Nintendo-based web browsers.

[32] The browser's use of compression and encrypted proxy-based technology to reduce traffic and speed page display has the side effect of allowing it to circumvent several approaches to Internet censorship.

This is almost certainly due to the Chinese government being concerned that users are using Opera Mini to bypass the Great Firewall of China.

Opera Mini uses a server to translate HTML, CSS and JavaScript into a more compact format.

[4][40] The turbo and mini modes reduce the amount of data transferred, thereby also increasing speed on slower connections.

The turbo and uncompressed modes use the "WebView" on Android and the WebKit layout engine on iOS.

[49] As Opera Mini reformats web pages, it does not pass the Acid2 standards compliance test.

[50][51] Opera Mini supports bi-directional text and can correctly display right-to-left scripts such as Arabic and Hebrew in addition to languages written left-to-right.

[49] Opera Mini can send content in bitmap image form if a font required is not available on the device, which is useful for indic scripts.

When browsing the Web in Opera Mini mode, JavaScript is processed by the proxy server, and is merely rendered on the device.

JavaScript will only run for a couple of seconds on the Mini server before pausing, due to resource constraints.

[54] On Opera Mini, before the page is sent to the mobile device, its onLoad events are fired and all scripts are allowed a maximum of two seconds to execute.

The proxy server then executes the JavaScript and returns the revised page to the mobile device.

However, Opera Mini's Extreme mode does not offer true end-to-end security when visiting HTTPS encrypted websites only for data saving purpose.

Opera Mini servers act as a proxy which compresses and renders the data of web pages before sending it to users.

The display may be toggled between portrait and landscape mode by keystrokes, or will switch automatically on phones with orientation sensors.

[64] Opera Mini supports only one font,[49] which can be set to "Small", "Medium", or "Large" size.

When activated, Opera Mini servers try to filter out advertisement before rendering the page and sending it to the client phone.

[67] Opera Mini relies on data centers processing the Web page before sending it back to the phone in a compressed binary form.

Opera Software operates data centers in the United States, Norway, China, Korea, Poland and Iceland.

[70] While not officially supported on ChromeOS, Vlad Filippov published a guide that teaches how to run Opera Mini inside the Chromium browser.