External links must look different from in-site links so the jump can be predicted

What it is

An in-site link keeps the person inside the same trust boundary and the same navigation. An external link sends them to another domain, where the back chain, the look, and who handles the data all change. Visual distinction lets someone judge “I will leave here” before the click, rather than recognizing a foreign chrome after the fact. What it forecasts is whether the destination is still this site—not whether a new window will open, and not whether the link is dangerous.

Why it happens

The default prediction for a link is “still in this product.” A mass of in-site blue underlines trained it. An unmarked outbound link falsifies the prediction; the first frame of a foreign brand is read as “the site redesigned” or “I was redirected.” Information scent breaks before the jump: people judge the next hop from residue on the current page, and an outbound hop does not belong to that residue. A distinct mark (icon, the word “external,” a domain preview) puts scent back before activation.

Colour alone is not enough. Colour blindness, high-contrast themes, and visited-link colour eat an “external colour.” If the new-window icon and the external icon are the same arrow, two exceptions are welded: in-site help in a new window, off-site in place, and neither consequence can be predicted. Screen-reader users need “external” in the name, or the visual icon is nothing to them. Occasional outbound links in a paragraph need per-link marks; a whole page of outbound directory is clearer with a page-level statement than with an icon on every item.

Studying it

Give the same links three looks: unmarked, icon only, icon plus “external” or the domain. Ask before the click “where will this go,” and score surprise after.

• Dependent variables: accuracy of in-site/off-site judgment before click, surprise after the jump, whether a screen reader hears “external” before activation.
• Independent variables: form of mark, whether it also means new window, density of outbound links.
• Methodological note: staff who know this site’s URL patterns will judge from the hover status bar and overestimate unmarked predictability. Forbid the status bar, or test on a touch screen. Do not mix this task with a risk-confirm for outbound links, or “distinguishable” gets run over by “is it dangerous.”

Where it stops holding

Hyperlinks in user content (comments, chat) are huge and cannot be hand-reviewed; per-item icons turn the body into noise. A uniform rule (user content defaults to the outbound style) beats manual marks. Subdomains, CDNs, and the auth domain used for login are external in engineering and still “this product” in the user model; marking them external over-warns. A pure icon with no text equivalent is undistinguished for screen-reader and some low-vision users.

Applying it

• Give off-site links a mark next to the visible label that in-site links do not have, and include “external” in the accessible name. Do not use colour alone.
• Keep the outbound mark and the new-window mark separate; when both happen, say both.
• Hover or long-press may preview the target domain as a supplement to the mark, not a replacement.
• Verify: give someone uninvolved a body mixing in-site and off-site links, forbid the status bar, and have them classify each before clicking. An outbound link classed as in-site, or a screen reader that does not hear “external” before activation, is undistinguished. Mix in a few in-site help links that open new, and confirm the outbound icon was not reused on them.

Related

• Within the group: G4.08.2 Leaving with unsaved changes must intercept, not silently discard · G4.08.3 Jumping to another domain is a trust transfer; high-risk cases need a second confirm · G4.08.4 Leave prompts only where data would actually be lost; overuse numbs people · G4.08.5 Outbound jumps may send referrer data; sensitive cases must disclose or block
• Adjacent: G4.04 New window versus in-place navigation · G2.08 Predictability of navigation items · E1.08 Links versus buttons
• Search terms: external link · outbound affordance · link destination