Cookie Size Checker
Inspect Cookie / Set-Cookie attributes and consistency in your browser. No input is sent to a server. Use it for first-pass operational troubleshooting.
Status
Runs in your browser. No input is sent to a server. Use this as a first-pass diagnostic step.
How to use
Paste a Cookie header or cookie string and click “Parse”. Size breakdown is shown.
Notes (this tool)
- This is an estimate. Actual limits depend on servers/proxies.
About this page
What does this tool do?
Paste a Cookie header (or cookie string) to estimate total size and per-cookie sizes.
Useful for diagnosing “header too large” or dropped request issues.
Typical use cases
- Check whether cookies are bloated
- Understand total cookie size across multiple keys
- Assess risk of server/proxy header limits
Guidance and notes
- Limits vary by browser/server/proxy
- This tool estimates byte size of the input string
- Storage limits for Set-Cookie are separate
What this tool does
- Estimate total Cookie header size
- Per-cookie size breakdown
- Basic duplicate-name detection
Debugging workflow (recommended)
- Paste Cookie or Set-Cookie values
- Review attributes such as Secure, HttpOnly, and SameSite
- Check Domain and Path conflicts with related tools
Operational notes
- Behavior can vary with browser implementation differences and default changes.
- Duplicate cookie names and Path or Domain differences often cause operational issues.
Referenced specs
- RFC 6265 (HTTP Cookies)
FAQ
Is there a practical cookie size guideline?
It depends on environment, but keeping each cookie small and monitoring total size is safer.
What should be reduced when size is too large?
First remove unnecessary tracking/state cookies, then move bulky state to server-side sessions if needed.
References
Next to view (diagnostic order)
These links are generated from site_map rules in recommended diagnostic order.
- How to Diagnose Set-Cookie Not Persisting — Isolate cookie persistence failures by checking Domain/Path/Secure/SameSite in order
- 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
- How to choose cookie tools — Route Set-Cookie, Domain-Path, SameSite, conflict, and size checks by symptom
- Cookie Domain/Path Matcher — Evaluate cookie send conditions by Domain/Path/Secure
- Cookie Parser — Split Cookie headers into key=value pairs
- SameSite Cookie Simulator — Simulate cookie send behavior from SameSite and request context
- HTTP Header Parser — Parse raw headers into structured lists
Same-theme links
Response Header Diagnostics
Step through raw headers to inspect Retry-After, Server-Timing, Link, and Content-Type
- HTTP Header Parser — Parse raw headers into structured lists
- Response Headers Parser — Parse response headers into structured data
- Set-Cookie Inspect — Parse Set-Cookie attributes and review delivery policy
- Cookie Domain/Path Matcher — Evaluate cookie send conditions by Domain/Path/Secure
- SameSite Cookie Simulator — Simulate cookie send behavior from SameSite and request context
- Set-Cookie Conflict Checker — Detect same-name cookie conflicts and overwrite risks
- Retry-After Inspect — Parse Retry-After and inspect retry wait behavior
- Server-Timing Inspect — Parse Server-Timing and inspect latency metrics
- Link Header Inspect — Parse Link headers and inspect rel/as/type
- Content-Type Inspect — Parse Content-Type and inspect MIME/charset
- X-Content-Type-Options Inspect — Parse X-Content-Type-Options and validate nosniff
- HTTP Status Inspect — Analyze HTTP status codes and suggest handling direction
Example
Cookie: sid=abc; theme=dark; lang=en