A letter grade is the at-a-glance summary the site readiness audit emits. It compresses the nine per-category scores into a single number, then into a letter:
| Score | Grade |
|---|---|
| 90-100 | A |
| 80-89 | B |
| 70-79 | C |
| 60-69 | D |
| below 60 | F |
What the score is actually
The overall score is a weighted average of the nine category scores. Each category contributes equally — security carries the same weight as schema, which carries the same weight as performance — so a high-leverage category lifting (or tanking) one score by 30 points moves the overall by ~3.3 points.
When the grade is misleading
The grade is a useful headline but the per-category breakdown is where the actionable signal lives. A site can score B 85 while having a complete security failure (36/100) because the other eight categories average it back up. Always read past the letter.
For audit history, the grade is what we plot — the sparkline on the per-project audit page shows the letter on each tick, so a sudden drop is visible even at low resolution.