What this analysis does
Paste campaign HTML to measure payload size, identify tracking surfaces, spot accessibility gaps, detect risky CSS and produce a prioritized optimization plan.
Preflight is most useful on the final HTML handed to the sender, after template rendering and link decoration. It is an evidence check before release, not a promise that every mailbox client will render the message identically.
Test the payload that will actually be sent
Export the production HTML after variables, reusable components and conditional content have been resolved. Development templates often understate final size because an ESP can inline CSS, rewrite links, add tracking parameters or duplicate markup during compilation.
The analyzer measures source weight and highlights clipping pressure, but it keeps a safety margin instead of treating one byte threshold as universal. Transport encoding and send-time transformations can change the delivered representation.
- Use a representative fully populated campaign.
- Remove secrets and personal data before pasting.
- Repeat the check after the sending platform transforms the template.
Treat accessibility and compatibility as release criteria
Missing alternative text, unclear link labels and fragile document structure affect people before they affect a score. Compatibility warnings identify markup that deserves testing across the mailbox clients in your audience; they are not proof that every version of a client will fail.
Prioritize defects that hide the message purpose, call to action or required legal information. Decorative differences should not outrank a missing accessible name or a broken destination.
Run the focused accessibility auditReview the accessible email workflow
Review tracking and external resources without loading them
The scan inventories remote images, links and tracking-shaped markup as text. It does not fetch those resources, which avoids triggering pixels during analysis. A discovered URL still needs an ownership and privacy review; the presence of a small image alone is not a verdict about intent.
Check redirect destinations in the sending platform, document approved domains and verify unsubscribe behavior from a real delivered message before launch.
Example: final HTML is larger than the template
Evidence supplied
The source template is compact, but the ESP output includes inlined CSS, per-link tracking and repeated responsive rules.
How to read the result
Preflight measures the transformed HTML, identifies the largest pressure sources and separates size risk from accessibility and link findings.
Known limits
- The tool does not execute JavaScript or load remote images and stylesheets.
- It cannot reproduce every proprietary rendering engine or mailbox-client version.
- Inbox placement and reputation are not inferred from HTML quality alone.
Common questions
Should I paste the source template or the sent HTML?
Prefer the final generated HTML. Test the source earlier for development feedback, then repeat after ESP transformation.
Does a passing result guarantee no Gmail clipping?
No. Send-time changes and encoding can alter size, so retain headroom and verify a delivered message.
Are external images downloaded during the scan?
No. Remote resources are inventoried from markup without being fetched.