Will removing nosniff fix the issue?

Not as a root fix. Keep nosniff and correct the Content-Type first.

What commonly causes JS to be served as text/html?

Typical causes are missing asset URLs returning HTML error pages and header rewrites by CDN/proxy layers.

When browser consoles show MIME type errors, the fastest path is to verify resource payload, Content-Type, and nosniff together.

1) Capture status, Content-Type, and X-Content-Type-Options with Response Headers Parser
2) Verify MIME type and charset using Content-Type Inspect
3) Validate effective nosniff and detect duplicate values with X-Content-Type-Options Inspect
4) Check missing or overwritten headers across delivery layers via Security Headers Audit
5) Confirm there is no 404/302/error-page HTML fallback with HTTP Status Inspect

Will removing nosniff fix the issue?: Not as a root fix. Keep nosniff and correct the Content-Type first.
What commonly causes JS to be served as text/html?: Typical causes are missing asset URLs returning HTML error pages and header rewrites by CDN/proxy layers.

These links are generated from site_map rules in recommended diagnostic order.

Response Headers Parser — Parse response headers into structured data
Content-Type Inspect — Parse Content-Type and inspect MIME/charset
X-Content-Type-Options Inspect — Parse X-Content-Type-Options and validate nosniff
Security Headers Audit — Audit presence of major security headers
HTTP Status Inspect — Analyze HTTP status codes and suggest handling direction
Symptom-Based Diagnostic Guide (Start Here) — A central hub that routes cache/CORS/JWT/MIME incidents into shortest symptom-first diagnostic paths
How to Diagnose Missing 304 Responses — Trace ETag/Last-Modified and If-* round trips to isolate missing 304 behavior
How to Diagnose Stale Content After Deployment — Check cache policy by HTML/API/static assets to isolate stale deployment issues quickly

Operational incident scenarios that route you into the shortest diagnostic path

Symptom-Based Diagnostic Guide (Start Here) — A central hub that routes cache/CORS/JWT/MIME incidents into shortest symptom-first diagnostic paths
How to Diagnose Missing 304 Responses — Trace ETag/Last-Modified and If-* round trips to isolate missing 304 behavior
How to Diagnose Stale Content After Deployment — Check cache policy by HTML/API/static assets to isolate stale deployment issues quickly
How to Diagnose CORS Preflight Failures — Fix preflight failures by validating OPTIONS responses, Allow-* directives, and origin rules in order
JWT 401/403 Diagnostic Playbook — Separate 401 and 403 using Authorization, WWW-Authenticate, claims, and signature checks
How to Diagnose Retry Storms on 429/503 — Isolate Retry-After parsing and client implementation gaps to stop excessive retries
How to Diagnose Set-Cookie Not Persisting — Isolate cookie persistence failures by checking Domain/Path/Secure/SameSite in order
How to Diagnose Lost Login After OAuth Return — Isolate cookie-delivery failures after IdP return across SameSite, Secure, Path/Domain, and collisions
How to Diagnose Same-Name Cookie Collisions — Resolve unstable behavior by tracing same-name cookie path/domain variants, overwrite order, and send collisions
Cookie Incident Operational Checklist — Standardize response from triage to permanent fixes across storage failures, OAuth return issues, and same-name collisions