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19th May, 2018

By SpareChange

SpareChange is a service which helps you setup bitcoin mining on your user’s browser. The idea is that whenever someone visits your website, instead of showing them an advertisement, you use their CPU power to hash Monero cryptocurrency. Let see in our review how feasible this is.


For this review we’re testing SpareChange’s WordPress plugin. Before installing, you’ll need a SpareChange account. After creating an account and installing the plugin from wordpress.org, head over to Sidebar > SpareChange Options. Enter the API key(you can get this from SpareChange’s dashboard) and you’re good to go.

SpareChange 1
SpareChange 1

There’s a lot of functionality missing from the plugin. There should be options to show opt-in before the mining starts, some sort of throttling on mobile devices(because they are very underpowered and hashing XMR could slow down the browser), notification to show that mining has started, etc.

As for now I recommend including sparechange.js directly from their main website and embedding it instead of downloading this plugin.

Under the hood

I checked the plugin files to see if there’s no funny business going now. Luckily, its pretty straightforward. The plugin files only set the options and load sparechange.js

This javascript is what does the heavy lifting. After setting up the plugin, head over to your website and open up console. The console will show that the js has loaded and it is testing for the best way to run the miner(it uses wasm apparently). Once that’s done, the console will output Starting miner. This is when the actual mining starts.

Ethical concerns

SpareChange is a pretty barebone plugin and they don’t have any functionality to show whether the miner is running or not. This means that it it up to the site owner to let their users know their browser is hashing crypto behind the scenes.

Personally, I would suggest showing a banner stating that your browser will be used for hashing crypto instead of showing ads.


You need to hash a lot of XMR for it to be economically viable. I’m sure if this strategy could work. This is how my SpareChange account dashboard looked like after using it for some time.

At this rate, I'll be a millionaire in about 833.3 centuries
At this rate, I’ll be a millionaire in about 833.3 centuries

Based on our napkin mathematics, we figured if each user on your site generates 0.0001USD and there are about 1,00,000 users on your site monthly, it will take you a bit more than 8 centuries to become a millionaire.

Well not 8 centuries really, because each user can have multiple sessions and lastly, what if the value of XMR goes up?

Good for SpareChange that adblockers(AdblockPlus atleast) does not disable miner scripts by default but they could in the future. That could make this business model very risky.

As for the plugin itself, it is very barebones at the moment. I would suggest waiting for some time before they add more features.


The SpareChange plugin has potential but its missing a lot of functionality currently to be practically useful.


Helpful disclosure

Our works are supported by earning an affiliate commision
when readers choose to purchase a plugin based our reviews.

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