Two ARNs that look almost identical at a glance — same length, same general shape — can differ in exactly one field, and spotting which one by eye is slow and error-prone, especially with long resource ids or nested paths. ARN Comparison Tool takes two ARNs and lines up their fields side by side, marking each one same or different, so the one field that actually changed is immediately obvious instead of buried in a wall of near-identical text.
Both ARNs are parsed with the same logic used throughout these tools: the fixed header up to the fifth colon splits into partition, service, region and account, and everything after that is the resource, further split into a resource type and resource id on whichever of / or : appears first. That gives six comparable fields — partition, service, region, account, resource type, resource id — and each one is checked independently, so two ARNs that differ only in account id show every other row as identical, while two ARNs from entirely different services show most rows as different, all without any manual field-by-field reading.
Comparing two ARNs only makes sense once both of them are actually valid ARNs to begin with, so parsing happens first and independently for each side. If either ARN does not meet the minimum shape — too few colon-separated fields, or a missing arn: prefix — no diff is attempted at all. Instead the tool reports specifically which of the two inputs failed (A, B, or both) and the exact parse error for each, so you are never shown a diff that quietly compares a real ARN against garbage, or two sets of garbage against each other, as if that were a meaningful result. This mirrors a broader principle across these ARN tools: a wrong answer that looks confident is worse than no answer with a clear explanation, and a field-by-field diff of an unparseable string would be exactly that kind of wrong answer.
The result is shown as a table with one row per field, one column for ARN A's value, one for ARN B's value, and a same/different indicator for each row — plus a top-line summary of whether the two ARNs are identical overall. Where a field differs, both values are shown in full rather than truncated, since the whole point is being able to read exactly what changed. A Copy button lets you pull the full comparison out as JSON for a ticket or a code review comment.
Typical uses include confirming that a resource ARN referenced in two different environments (staging vs. production, or two AWS accounts) really does point at the equivalent resource with only the account or region changed; checking that a policy update did not accidentally alter a resource type or id along with the field you meant to change; or simply verifying that two ARNs copied from different sources are, in fact, the same. The tool only compares the parsed fields of the ARN strings themselves — it has no way to know whether the underlying AWS resource still exists, or whether two structurally different ARNs happen to refer to the same real-world resource, since that would require contacting AWS, which this page never does. Everything runs locally in your browser, so the ARNs you compare — which often include real account ids — are never sent anywhere.