What is the mtm_consent cookie?
mtm_consent is an HTTP cookie set by Matomo (formerly Piwik), an open-source web analytics platform commonly used as a privacy-focused alternative to Google Analytics, including on self-hosted installations across the EU.
The cookie appears when a site uses Matomo's built-in consent feature ("Require cookie consent"), which is integrated directly into the JavaScript tracker (piwik.js / matomo.js) without requiring an external CMP. It is created as soon as a visitor accepts tracking through this internal Matomo mechanism.
What data it stores
The cookie's value is typically a timestamp marking when consent was given. The exact format can vary depending on the installed Matomo version.
The cookie is stored locally in the visitor's browser, on the domain of the site running Matomo (self-hosted) or on the domain of the chosen Matomo Cloud instance. It is not sent to third-party servers – the data stays within the infrastructure controlled by the site owner or their chosen Matomo Cloud provider.
What it is used for
The cookie's role is purely functional: it lets the Matomo tracker check, on each page load, whether the visitor has already given consent, so that statistical tracking (cookies such as _pk_id or _pk_ses) only starts after consent, without repeatedly prompting the visitor.
For site owners, this mechanism helps meet the legal requirement of not tracking visitor behavior before obtaining explicit consent.
Does it require consent?
In CookieFix's classification, mtm_consent is categorized as necessary (strictly necessary), since it does not track user behavior but merely stores a consent preference – functionally similar to a CMP's own consent-state cookies.
- Under GDPR and the ePrivacy Directive (implemented in Romania via Law 506/2004), strictly necessary cookies do not require prior consent, but must still be disclosed in the site's cookie policy.
- Site owners should clearly list this cookie for transparency toward visitors and data protection authorities, even though no separate opt-in is required.
- It should not be confused with Matomo's tracking cookies (
_pk_id,_pk_ses), which are statistical and do require explicit consent.
How to block or delete mtm_consent
Visitors can delete or block mtm_consent from their browser settings (Chrome, Firefox, Edge, Safari – per-site cookie management), but doing so will cause Matomo's consent prompt to reappear on subsequent visits.
For site owners running a CMP such as CookieFix alongside Matomo, it's important that Matomo's tracking scripts are automatically blocked until consent is given, and that Matomo cookies are correctly categorized (strictly necessary vs. statistics) in the banner, to avoid showing two conflicting consent mechanisms to the same visitor.
Frequently asked questions
No, it is classified as strictly necessary because it only stores the fact that a visitor expressed a preference, not their behavior. It still needs to be listed in the site's cookie policy.
mtm_consent stores the consent state, while cookies like _pk_id or _pk_ses actually track sessions and visitors for statistics, which is why the latter require explicit consent.
Matomo uses a very long duration to avoid repeatedly asking the same visitor for consent, similar to how many platforms store an already-given preference long-term.
Yes, but the site owner needs to set things up correctly: consent for Matomo's statistical tracking should be managed through the CMP, with Matomo's built-in prompt disabled or aligned to it, to avoid showing visitors duplicate consent requests.