Re. the "pastebin somewhere" idea: For our "SPARQL Lab", we use a mechanism to load queries from Github (or alternatively from an internal git repository). That has the additional advantage that the queries can be updated under a constant URL, discussed, forked etc. For details and links see https://zbw.eu/labs/en/blog/publishing-sparql-queries-live

Probably depends on T225701.

For checking exactly one item in a simple way, see also CheckShEx UserScript (based on PyShExy API).

Thanks - I've moved the requests to https://www.wikidata.org/wiki/Wikidata:SPARQL_federation_input#Incoming_nominations and added two endpoints with derived datasets from GND

OK, I did not think about licenses - sorry!

Examples for the federated query use case see at https://github.com/zbw/sparql-queries/tree/master/wikidata#power-queries (queries with econ_pers or ebds in name). The intermediate set fed into Wikidata was about 450,000 GND IDs. Currently, that requieres setting up a custom Wikidata endpoint.

This is not only a question of the tools in use, but also it also imposes length restrictions to queries, which are transmitted in the GET URL.

Another argument for enabling POST requests is, that GET requests / URLs are limited in length. The exact limit depends (see http://stackoverflow.com/questions/417142/what-is-the-maximum-length-of-a-url-in-different-browsers), but often seems to be about 2000 characters. I hit this in the past in several real queries.