What UTM parameters do
UTM parameters are tags appended to a URL that analytics tools read on arrival. Without them, visitors from your newsletter, a partner blog and a paid post all collapse into vague buckets like "direct" or "referral" — and you lose the ability to tell which effort actually worked.
They're invisible to the visitor's experience and don't affect the page they land on. The five standard parameters are utm_source, utm_medium, utm_campaign, utm_term and utm_content, and they've been the de facto standard since Urchin — the "U" in UTM — became Google Analytics.
Source, medium and campaign: the three that matter
Source is where the link lives: newsletter, twitter, partner-blog. Medium is the type of channel: email, social, cpc, referral. Source and medium are the pair analytics reports are built around, and both should be on every tagged link.
Campaign groups links that belong to the same initiative — spring-launch, black-friday — so you can measure the whole effort across channels. Term is for paid keywords, and content distinguishes variants: use it to tell a header button from a footer link in the same email, or version A from version B in a test.
Consistency matters more than cleverness
UTM values are case-sensitive in most analytics platforms. Email, email and E-mail become three separate rows in your reports, splitting the data for the same channel — which is exactly the confusion you adopted UTMs to avoid. This builder lowercases values and converts spaces to hyphens automatically for that reason.
Agree a naming convention before you start tagging and write it down. A short shared document listing your approved mediums (email, social, cpc, referral, display) and how campaigns are named will save you far more time than it costs.
Two mistakes worth avoiding
Never tag internal links. Adding UTM parameters to links between pages on your own site starts a brand-new session in most analytics tools, wrongly attributing the visitor to that campaign and destroying your understanding of the original source. Use internal link tracking or events instead.
Be careful with tagged URLs in indexable places. If a tagged link gets crawled and indexed, you can end up with duplicate URLs for the same page competing in search. A self-referencing canonical tag on the clean URL protects against this — the meta tag generator produces one.
Tagged links are also long and ugly. For anything a human will see — printed material, social bios, spoken URLs — run the tagged link through a shortener, which preserves the parameters through the redirect.