What this analysis does
Paste final campaign HTML to measure raw source weight and expose comments, redundant structure and other markup pressure. The tool keeps the broader preflight context visible because send-time systems can add markup after your local template is produced.
When a message exceeds the size a client will render inline, the remainder is hidden behind an additional click. Everything below that boundary — footer, legal text, unsubscribe link — stops being reliably visible, and the measurement that predicts it is source size, not visual length.
Source weight, not perceived length
A visually short campaign can carry a heavy payload. Repeated inline style declarations, builder comments, hidden preheader structures, nested tables and long tracking parameters on every link all add source bytes without adding visible content. A long message built cleanly can be lighter than a short one built by a visual editor.
Remotely hosted images do not count toward the source size, because they are referenced rather than embedded. Inlined base64 images do count, and a single inlined logo can consume a large share of the available budget on its own.
- Referenced images do not add to source size; inlined base64 images do.
- Repeated inline declarations are usually the largest avoidable cost.
- Tracking parameters on every link accumulate quickly.
Clipping hides compliance-relevant content
The consequence is not only cosmetic. Unsubscribe links, legal disclosures and physical address requirements typically sit in the footer, which is exactly what disappears first. A message that clips can therefore present a compliance problem as well as a usability one.
Analytics are distorted at the same time. Clicks on content below the boundary are suppressed because most recipients never expand the message, which makes engagement data from a clipped campaign misleading rather than merely lower.
Leave margin for platform injection
The HTML pasted into a builder is not the HTML that reaches the recipient. Platforms add tracking parameters, unsubscribe blocks, footers and sometimes rewrite styles, and all of that arrives after any check performed in the editor.
A source size close to the threshold should therefore be treated as failing even when a preview reports it as passing. Optimize in the safe order — comments, duplicate declarations, unused wrappers — before touching structural tables or client compatibility code.
Read the clipping guideCompare size against the previous release
Example: passing in the editor, clipped in production
Evidence supplied
A template measuring just under the threshold in the sending platform preview.
How to read the result
The analysis reports the remaining margin as insufficient, because platform-injected tracking and footer content are added after the preview is generated and routinely consume more than the remaining headroom.
Known limits
- Measurement covers the HTML supplied; the platform will add content afterwards.
- Client thresholds are behavioural rather than formally specified and can change.
- A passing measurement does not guarantee correct rendering in every client.
Common questions
Do images count toward the size?
Remotely referenced images do not. Base64-inlined images do, and they are frequently the single largest contributor.
How much margin should I leave?
Enough to absorb platform injection. Treating a measurement close to the threshold as failing is the safer working rule.
What should be removed first?
Comments, duplicate style declarations and unused wrapper markup. Structural tables and client-specific compatibility code should be changed only with rendering verification.