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Header Diff

Compare HTTP headers side by side and highlight differences.

Left Headers

Right Headers

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Header Diff: complete usage guide

Compare two HTTP header sets to quickly identify changed security directives, caching rules, and proxy metadata across environments.

What this tool does

It parses `Header-Name: value` lines into comparable key-value entries.

It matches header names case-insensitively and highlights value differences.

It marks added, removed, modified, and unchanged headers with clear status labels.

It helps troubleshoot deployment drift between local, staging, and production responses.

Typical use cases

Compare response headers before and after CDN or proxy changes.
Audit security header rollouts such as CSP and HSTS updates.
Validate cache-control policy differences between environments.
Inspect API gateway behavior after middleware refactors.
Create evidence snapshots for incident postmortems.

Input examples

Left headers

Content-Type: application/json
Cache-Control: no-cache

Right headers

Content-Type: text/html
Cache-Control: max-age=3600

Security sample

Content-Security-Policy: default-src 'self'

Output examples

Modified header

Content-Type changed from application/json to text/html

Added header

X-Forwarded-For added on right side

Diff summary

Removed 1, modified 2, added 1, unchanged 3

Common errors and fixes

Missing colon separator in input line

Use `Header-Name: value` format for each row.

Duplicate header names collapse unexpectedly

Merge duplicate values explicitly before comparison if needed.

Whitespace around values causes false diffs

Trim and normalize header lines before pasting.

Multi-line folded headers parsed incorrectly

Flatten folded headers into a single normalized line first.

Comparing request and response headers together

Compare matching header contexts only.

Security and privacy notes

Header comparison is local and does not transmit pasted values.
Remove auth tokens and cookies from shared examples.
Do not expose internal infrastructure header names publicly.

Step-by-step workflow

Start with a minimal input for Header Diff and verify baseline behavior first.
Make assumptions explicit: encoding, delimiter strategy, and timezone.
Change one variable at a time and compare output diffs.
Keep one verified output snapshot as a team reference.

Quality checklist before sharing output

Confirm Header Diff output is deterministic across repeated runs with identical input.
Check boundary inputs (empty values, long fields, invalid characters).
Remove sensitive data before sharing output externally.
Verify final rendering on both desktop and mobile viewports.

Operational notes

Header Diff should be treated as a repeatable validation step before merge, release, and handoff.

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Frequently asked questions

Are header names case-sensitive in this diff?

No, names are compared case-insensitively.

Can I compare security header changes?

Yes, this is useful for CSP, HSTS, and related checks.

Why is one header marked removed?

It exists on one side only and is absent on the other.

Should I include cookies in shared diffs?

Avoid sharing real cookie values; redact sensitive data first.

Can this validate header correctness?

It highlights differences; compliance validation still needs policy checks.