Alternatives · each names its own limits
Free alternatives
Every page below says which part of the other product it replaces and which part it does not. Where the other tool is free and official, or cheaper for your usage, the page says that too.
Screaming Frog SEO Spider
The first thing people open Screaming Frog to do: point it at a URL and read what is wrong with that page.
Ahrefs Site Audit
Auditing one URL without a subscription, and seeing the finding list rather than a health score.
Google's Rich Results Test
Testing JSON-LD against the feature requirements, with the failing property named and the rule quoted.