Klaro! vs. Zest
Klaro! is the best-known open-source consent manager: BSD-3 licensed, born from a research project, maintained by kiprotect. If you went looking for a free, self-owned consent tool before Zest existed, Klaro is probably what you found. Zest is the newcomer in the same weight class: MIT-licensed, 16KB, zero config required to start.
This is the honest comparison between two tools that both cost nothing and both belong to you.
Head to head
| Klaro! | Zest | |
|---|---|---|
| Price | Free, open source | Free forever, open source |
| License | BSD-3 | MIT |
| Script weight | ~57KB min+gzip, includes styles and translations | 16KB gzipped, styles included |
| Setup | Write a config file: declare every app, purpose, and cookie pattern | Paste one script; defaults work out of the box |
| Script blocking | Manual: you tag or declare each script in the config | Automatic in safe mode: known trackers are gated with zero listing, plus manual and strict modes |
| Geo rules | Not built in | Built in: geo: true maps each visitor to GDPR, UK GDPR, 19 US state laws, LGPD, PIPEDA and more |
| Consent Mode v2 | Not built in | One config flag |
| GPC / DNT | Not built in | respectDNT with configurable behavior, GPC honored |
| Languages | 23+ out of the box, fully customizable translations | 12, auto-detected from the visitor’s browser |
| UI | React-rendered consent notice and modal | Shadow DOM, themes, no styling conflicts with your site |
| Config surface | One JS file you author and maintain | Defaults plus optional window.ZestConfig overrides |
Where Klaro! wins
- 23+ languages with deep internationalization support, and adding your own translations is genuinely easy.
- Mature and battle-tested: public sector, universities, and NGOs have run it for years.
- You declare each app’s cookie patterns, so cleanup on withdrawal (deleting
_gaetc.) is explicit and thorough. - The consent manager works without its UI: import
klaro/dist/cmand render your own. Zest has a headless build too, but Klaro has shipped one longer.
Where Zest wins
- Sixteen kilobytes. Klaro ships React plus styles plus all translations.
- Auto-blocking: known trackers are gated before you write a single line of config. With Klaro, an undeclared script runs.
- Geo decisions, Consent Mode v2, and GPC are config flags, not integration projects.
- Shadow DOM theming: the banner never fights your CSS, and it follows the visitor’s system theme by default.
Pick Klaro! if
You need a language Zest does not ship yet, or you want the most battle-tested open-source consent tool with years of public-sector deployments behind it. Klaro is a fine tool and choosing it over a subscription CMP is already a good decision.
Pick Zest if
You want consent working in the next ten minutes and you want the boring parts (blocking, geo, consent mode) handled by defaults. Configure the banner in the playground and paste one line.
FAQ
Are both really free? Yes. BSD-3 vs MIT are both permissive licenses; neither has a paid tier or a hosted upsell. The difference is shape, not price.
Can I migrate from Klaro to Zest?
Yes. Take Klaro’s app list, add the tracking domains to blockedDomains or rely on auto-blocking, and paste the Zest snippet where the Klaro config was. Visitor choices reset once.
Why is Zest smaller? No React, no bundled translation set for 23 languages, and a UI built in Shadow DOM with minimal styles. Zest ships 12 locales; a single-language build is smaller still.
Does Klaro block scripts automatically?
It manages scripts you declare or tag with data-name attributes. Anything you forget to declare runs without consent. Zest’s safe mode gates known tracker domains automatically, so forgetting is harder.
* Pricing and plan details for third-party products change often. This page reflects what we could verify on October 28, 2026 — check the vendor's current pricing before you decide.