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What the two platforms actually expose
TikTok renders a public profile shell for any handle, with follower and video counts visible without a session. Instagram is stricter: public accounts show a limited preview, private ones only confirm that the handle exists.
That asymmetry sets the realistic goal. You are looking for evidence that connects two accounts, not for a tool that jumps from one to the other, because no such tool exists.
The handle-first method
Start by checking whether the same string resolves on both platforms. It often does, because people register the handle they already know before they start posting.
If the identical handle is taken by someone else, look at the small set of variants people actually use: the handle with a trailing dot or underscore, the name plus a year, or the TikTok handle with "ig" appended. Check those specific strings rather than guessing at length.
Pivots that come from the person, not from you
The reliable links are the ones the account owner published. A TikTok bio that mentions another handle, a link-in-bio page listing both accounts, a photo posted to both, or a caption that crosses over are all self-declarations.
Where no such link exists, a matching handle plus a matching avatar is a reasonable hypothesis, and nothing more. If the account has a distinctive name, an unusual posting style, or the same three friends interacting, weight that — but describe it as inference when you write it down.
When the accounts do not connect
Sometimes they simply do not. People keep platforms deliberately separate, and a private Instagram with no cross-references is not evidence of anything except privacy settings working.
Do not manufacture a connection from a shared first name or a similar aesthetic. A wrong identification is worse than an incomplete one, because it attaches a real accusation to the wrong person.