Does c15t support Google-certified CMP like Didomi?

No, per vendor docs. Didomi documents Google-certified CMP support. c15t does not.

Do c15t and Didomi block trackers before consent?

Both held trackers back in every check. Each check loads the page. Then it looks for trackers that ran, cookies that the page set or data that left the page before the visitor chose.

c15t vs Didomi: cookie banner speed and features compared

Results forFramework

On emulated mobile, c15t showed its banner sooner, in a median 240 ms against 4.41 s for Didomi. c15t delayed the main content 872 ms less. Both held trackers back in every check. Per vendor docs, only c15t offers open-source code and a free tier. Per vendor docs, only Didomi offers a Google-certified CMP.

c15tinth

c15t Tested: 3.0.0-alpha.10
All c15t results

DidomiDidomi

Didomi Tested: Hosted
All Didomi results

Which is faster, c15t or Didomi?

Shorter bars are better. The exception is tracker blocking, where the bar shows the share of checks passed.

c15t and Didomi on the mobile (emulated) profile, Next.js 16
Question	c15t	Didomi	Difference
Banner appearsTime from navigation until the banner is visible on screen. Lower is better.	240 msFast	4.41 sSlow	c15t’s banner appeared 4.17 s sooner.
Page slowed byExtra time before the main content paints (LCP), compared with the same page without a consent manager.	+408 ms95% interval 396 ms to 420 msSmall	+1.28 s95% interval 1.26 s to 1.29 sLarge	c15t delayed the main content 872 ms less.
Click responds inTime from pressing Accept until the screen updates. Under 200 ms feels instant.	32 msOne visit measuredFast	16 msOne visit measuredFast	Didomi responded 16 ms sooner. Both are under 200 ms, which feels instant.
Blocks trackersChecks that no tracker runs, the page sets no cookie and no data leaves the page before the visitor chooses.	4 of 4 checks passedBlocked	4 of 4 checks passedBlocked	Both held trackers back in every check.
Adds to pageExtra data transferred during the first load, compared with the same page without a consent manager.	+112 KB95% interval: 112 KBModerate	+253 KB95% interval: 253 KBHeavy	c15t added 141 KB less to the first load.

“About the same” means that the two results fall within each other’s spread. We measure both against the same page without a consent manager. We do not publish a direct head-to-head interval yet.

Page vitals and load times

Lab detail for engineers. All values are medians on the mobile profile. Both CMPs ran on Next.js 16.

Page vitalsChange against the same page without a consent manager.
Metric	c15t	Didomi
TTFB	+15 mspage 21 ms	No measurable delaypage 5 ms
FCP	+28 mspage 268 ms	No measurable delaypage 248 ms
LCP	+408 mspage 3.86 s	+1.28 spage 4.72 s
CLS	No measurable shiftpage 0.00	No measurable shiftpage 0.00

Load timesMilliseconds from navigation.
Metric	c15t	Didomi
CMP script requested
CMP script loaded
Consent state known	1.98 s
Banner visible	240 ms	4.41 s

After AcceptMilliseconds from the click.
Metric	c15t	Didomi
Screen responds	32 ms	16 ms
Banner gone
Consent applied
Analytics active

Which features differ between c15t and Didomi?

Statuses come from each vendor’s documentation. Each status links to its source.

Verified by test
Per vendor docs
Partial
Not supported
Unknown

Features that differ between c15t and Didomi, from vendor docs
Feature	c15tc15t	DidomiDidomi
Only c15t · 3
Open sourceDeveloper	Apache-2.0 (vendor documentation, opens in a new tab)	Proprietary (vendor documentation, opens in a new tab)
Free tierPricing	Open source; hosted free plan (vendor documentation, opens in a new tab)	Contact sales (vendor documentation, opens in a new tab)
First-party SDKsFrameworks	Next.js, Vue, Nuxt, Svelte, SvelteKit, Astro, TanStack Start (vendor documentation, opens in a new tab)	Script tag only (vendor documentation, opens in a new tab)
Only Didomi · 1
Google-certified CMPStandards	Not on Google’s list (vendor documentation, opens in a new tab)	Per vendor docs (vendor documentation, opens in a new tab)

Same on both · 13

Features with the same status for c15t and Didomi
Feature	c15tc15t	DidomiDidomi
IAB TCFStandards	Per vendor docs (vendor documentation, opens in a new tab)	TCF v2.2 (vendor documentation, opens in a new tab)
IAB GPPStandards	GPP 1.1 (vendor documentation, opens in a new tab)	Per vendor docs (vendor documentation, opens in a new tab)
Google Consent Mode v2Standards	Per vendor docs (vendor documentation, opens in a new tab)	Per vendor docs (vendor documentation, opens in a new tab)
Global Privacy ControlStandards	Per vendor docs (vendor documentation, opens in a new tab)	Per vendor docs (vendor documentation, opens in a new tab)
Geo-targeted bannersCompliance	Per vendor docs (vendor documentation, opens in a new tab)	Per vendor docs (vendor documentation, opens in a new tab)
Script blockingCompliance	Per vendor docs (vendor documentation, opens in a new tab)	Tag-based (vendor documentation, opens in a new tab)
Consent recordsCompliance	With a backend (vendor documentation, opens in a new tab)	Per vendor docs (vendor documentation, opens in a new tab)
Cookie scanningCompliance	Via Inth Website Audit (vendor documentation, opens in a new tab)	Per vendor docs (vendor documentation, opens in a new tab)
Self-hostableDeveloper	Per vendor docs (vendor documentation, opens in a new tab)	Assets through your domain (vendor documentation, opens in a new tab)
Headless UIDeveloper	Per vendor docs (vendor documentation, opens in a new tab)	Per vendor docs (vendor documentation, opens in a new tab)
TypeScript typesDeveloper	Per vendor docs (vendor documentation, opens in a new tab)	React SDK only (vendor documentation, opens in a new tab)
Script tagFrameworks	Per vendor docs (vendor documentation, opens in a new tab)	Per vendor docs (vendor documentation, opens in a new tab)
First-party SDKsFrameworks	React (vendor documentation, opens in a new tab)	React (vendor documentation, opens in a new tab)

Should you choose c15t or Didomi?

We built these lists from the measured and documented differences above. Neither list is a recommendation.

Choose c15t if

You want open-source code and a free tier
You want a first-party SDK for Next.js, Vue, Nuxt, Svelte, SvelteKit, Astro and TanStack Start
A fast banner matters to you: c15t’s banner appeared 4.17 s sooner
Page load time matters to you: c15t delayed the main content 872 ms less

Choose Didomi if

You need a Google-certified CMP

What was tested?

Deployment: Both ran as hosted services. c15t ran against the hosted inth backend, not a local mock. Didomi ran from its vendor-hosted service. Network distance to each vendor is part of the result.

How we test: methodology cookiebench-v3.2.4