Inspector Score
How Inspector computes a single 0–100 score and letter grade across Performance, SEO, Security, Infrastructure, and Availability.
The VitalSentinel Inspector Score (shown in the UI on the score card and often shortened to Inspector Score) is a single 0-100 number summarizing the health of an inspected URL across five weighted pillars. It's shown at the top of every completed inspection alongside a letter grade (A-F) and a per-pillar breakdown.
Pillars
The score starts at 100. Issues subtract from one of five pillars, each with a fixed point budget:
| Pillar | Max Points | What it measures |
|---|---|---|
| Performance | 40 | Core Web Vitals, page weight, code efficiency, main-thread health |
| SEO | 25 | Crawlability, on-page fundamentals, JS rendering parity, structured data |
| Security | 20 | TLS/SSL, security headers, content security, cookie hygiene |
| Infrastructure | 10 | Caching, compression, protocol version, operational maturity |
| Availability | 5 | HTTP status, response time |
Each pillar contributes independently up to its cap. A page with poor performance but perfect security cannot score 0 - security still contributes its full 20 points.
The pillar card on the detail page shows each pillar's score, percentage, and a color band:
| Pillar % | Color |
|---|---|
| 90–100% | Green - pillar is healthy |
| 70–89% | Yellow - issues worth addressing |
| 50–69% | Orange - pillar is underperforming |
| 0–49% | Red - critical problems |
Grade Bands
The numeric score maps to a letter grade:
| Score | Grade | Meaning |
|---|---|---|
| 90–100 | A | Excellent - meets best practices across all pillars |
| 75–89 | B | Good - minor issues that don't materially harm users |
| 50–74 | C | Needs work - multiple warnings or one critical issue |
| 25–49 | D | Poor - critical issues across multiple pillars |
| 0–24 | F | Failing - page is broken, insecure, or invisible to search engines |
How Deductions Work
Every issue carries a severity that caps how much a single occurrence can deduct from its sub-pillar:
| Severity | Max deduction per issue |
|---|---|
| Critical | up to the full sub-pillar budget |
| Warning | 4 points |
| Info | 1.5 points |
When several issues hit the same sub-pillar, diminishing returns apply - the second issue costs 75% of the first, the third costs 75% of the second, and so on. This prevents a stack of minor problems in one area from disproportionately tanking the score, while still rewarding fixes for the worst issue first.
The sub-pillar score is capped at 0 - it never goes negative.
Fatal Penalty
Some failures are catastrophic - an expired SSL certificate, a 5xx server error, a noindex directive - and a normal pillar deduction wouldn't reflect their real impact. For these, Inspector applies a multiplicative cross-pillar penalty on top of the pillar deductions:
final_score = round(pillar_sum × 0.85^fatal_count)Each fatal issue knocks an additional 15% off the entire score.
| Fatal count | Multiplier | Score 95 becomes | Score 80 becomes |
|---|---|---|---|
| 0 | 1.00 | 95 (A) | 80 (B) |
| 1 | 0.85 | 81 (B) | 68 (C) |
| 2 | 0.72 | 68 (C) | 58 (C) |
| 3 | 0.61 | 58 (C) | 49 (D) |
A page can never get a clean A grade if it has an expired certificate or is blocked from search engines, no matter how good everything else is.
Fatal Issues
| Pillar | Fatal rule | Why |
|---|---|---|
| SEO | noindex directive active | Page tells search engines not to index it |
| SEO | robots.txt blocks the URL | Crawlers cannot access the page |
| SEO | robots.txt blocks Googlebot | Google specifically cannot reach the page |
| SEO | Robots directive changes after JS | Search engines may see contradictory instructions |
| Security | SSL certificate expired | Browser shows full-page security warning |
| Security | SSL hostname mismatch | Browser shows full-page security warning |
| Availability | Server returned 5xx | The page is broken |
| Availability | Server returned 404 | The page does not exist |
A fatal issue also zeroes its own sub-pillar in addition to applying the cross-pillar multiplier.
Worked Example
A staging site accidentally exposed to production: expired certificate, noindex tag, otherwise fine.
- TLS/SSL sub-pillar zeroed:
−8(fatal) - Crawlability sub-pillar zeroed:
−10(fatal) - Pillar sum:
40 + 15 + 12 + 10 + 5 = 82 - Two fatals → multiplier
0.85² = 0.7225 - Final score:
round(82 × 0.7225) = 59- Grade C
Without the fatal mechanism, a page with two browser-warning failures could still grade B. The penalty makes sure catastrophic problems are never masked by perfection elsewhere.
Domain Health Is Advisory
WHOIS findings (domain expiring soon, recently registered, privacy enabled) are surfaced as issues but do not deduct from the score and never trigger the fatal penalty. Domain registration is outside the technical control of the page and has no direct user-experience impact.
What's Not Counted
- No bonus points - the score starts at 100 and only goes down. There are no extra-credit items.
- CrUX no-data is not a penalty - a low-traffic URL with no field data is flagged as informational only.
- TTFB measured from three angles (CrUX, Chrome inspector, uptime) is intentionally counted in three sub-pillars without coalescing - a consistently slow server is confirmed from every vantage point.