Can I use any speed testing app?

Use the FCC app first. The FCC’s Speed Test app generates the only data that the FCC uses to challenge ISP claims of service and available speeds. Additionally, the data can be acquired for free by the public, governments and researchers. 

Other apps consider test result information proprietary, charge fees for access and often don’t share the raw data. The FCC will consider this information but it carries lest weight since it's much harder for them to verify.

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