HTTP Headers Analysis for https://api.substack.com

Detected Technologies from Headers

See all in URL Inspect 3

Cloudflare CDN

Substack

Express

HTTP Security Headers

Status

Strict-Transport-Security

Excellent

max-age=31536000; includeSubDomains; preload

Content-Security-Policy

Weak

frame-ancestors Analyze

Content-Security-Policy-Report-Only

Missing

Not configured Analyze

X-Frame-Options

Missing

Not configured

X-Content-Type-Options

Missing

Not configured

Referrer-Policy

Missing

Not configured

Permissions-Policy

Missing

Not configured

Recommendations

• Significantly strengthen CSP directives
• Add X-Frame-Options: DENY or SAMEORIGIN to prevent clickjacking
• Add X-Content-Type-Options: nosniff
• Add Referrer-Policy header (recommended: strict-origin-when-cross-origin)
• Consider adding Permissions-Policy to control browser features

Performance Headers

Connection

Performance

close

Transfer-Encoding

Performance

chunked

Vary

Performance

Accept-Encoding

connection: close
transfer-encoding: chunked
vary: Accept-Encoding

Caching Headers

Age

Caching

199

Cache-Control

Caching

no-cache

age: 199
cache-control: no-cache

Content Headers

Content-Type

Content

text/html; charset=utf-8

content-type: text/html; charset=utf-8

Server Headers

Server

cloudflare

X-Powered-By

Server

Express

server: cloudflare
x-powered-by: Express

CORS Headers

No CORS headers found

Cookies Headers

Set-Cookie

Cookies

set-cookie: ab_experiment_sampled=%22false%22; Max-Age=31536000; Domain=substack.com; Path=/; Expires=Thu, 25 Feb 2027 11:02:14 GMT; HttpOnly; Secure; SameSite=Lax
ab_testing_id=%22216f3997-7f0d-4eb9-b33a-6a134ae91d5f%22; Max-Age=31536000; Domain=substack.com; Path=/; Expires=Thu, 25 Feb 2027 11:02:14 GMT; HttpOnly; Secure; SameSite=Lax
__cf_bm=KrVZ4STrHjlOQ19AceVRWrzMR490uhJoz953K6LIBEs-1772017334-1.0.1.1-nklXcykCeDUkKdgsnymlQeE.zlBPXDzr_bFTn0wvsFfJEWm22B5dELZJQyVKSKAhN3SNlvNACcrkjjjTZT92UDYzDhGnhlzenrf5d2Dei5c; path=/; expires=Wed, 25-Feb-26 11:32:14 GMT; domain=.substack.com; HttpOnly; Secure; SameSite=None

Other Headers

Alt-Svc

Other

h3=":443"; ma=86400

Cf-Cache-Status

Other

HIT

Cf-Ray

Other

9d36b59358248248-IAD

Date

Other

Wed, 25 Feb 2026 11:02:14 GMT

Link

Other

URL

https://substackcdn.com

rel=preconnect

X-Cluster

Other

substack

X-Deploy

Other

a70936b1be

X-Served-By

Other

Substack

X-Service

Other

web

alt-svc: h3=":443"; ma=86400
cf-cache-status: HIT
cf-ray: 9d36b59358248248-IAD
date: Wed, 25 Feb 2026 11:02:14 GMT
link: <https://substackcdn.com>; rel=preconnect
x-cluster: substack
x-deploy: a70936b1be
x-served-by: Substack
x-service: web

Recommendations

Enable compression (gzip/brotli) to improve performance

Consider removing X-Powered-By header to hide server technology