> ## Documentation Index
> Fetch the complete documentation index at: https://docs.timeback.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Evaluating apps

> How Timeback measures app quality

Timeback operates on a simple principle: **if students are not learning, it is the system's fault.** Apps are evaluated the same way.

| Dimension                      | What matters                                       |
| ------------------------------ | -------------------------------------------------- |
| **Granularity**                | One teachable unit at a time                       |
| **Instruction quality**        | Clear explanations, worked examples, minimal noise |
| **Mastery truthfulness**       | "Completed" means mastered                         |
| **Coverage and rigor**         | Aligned to real external tests                     |
| **Efficiency**                 | Fewer hours to reach the same verified outcome     |
| **Hole-filling compatibility** | Targeted remediation is possible when gaps show up |

If an app performs well on engagement but poorly on externally validated outcomes, the closed loop forces the conversation back to instruction, mastery, and signal integrity.

<CardGroup>
  <Card title="Non-negotiables" href="/beta/about-timeback/concepts/non-negotiables">
    The rules every app must follow.
  </Card>

  <Card title="Integration levels" href="/beta/build-on-timeback/integration-levels">
    Level 1 vs Level 2 requirements.
  </Card>
</CardGroup>