How do I check the file size first?

Use HEAD: curl -I URL . The Content-Length header is the resource size.

416 Range Not Satisfiable: HTTP Status Code Meaning, Causes, and Fixes

What 416 Range Not Satisfiable means

416 Range Not Satisfiable means the client sent a Range header asking for bytes that do not exist in the resource. Most commonly: requesting bytes 5000-6000 of a file that is only 4000 bytes long. The response should include a Content-Range header indicating the actual size, so the client can adjust and retry.

When servers should return it: Return 416 when the Range header asks for bytes outside the resource bounds.

Common causes

Resume of a download where the file changed size
Client miscomputed the range
Off-by-one in Range header construction

How to fix 416 Range Not Satisfiable

Re-fetch the resource size with HEAD or a 0-byte range
Recompute the range based on the current size
For resumable downloads, store the original size and verify before resuming

Example response

curl -i -H "Range: bytes=10000-20000" https://example.com/small.txt

HTTP/2 416
content-range: bytes */500
content-type: text/plain
Range out of bounds

More references

For a one-page reference of all HTTP status codes, see the HTTP cheat sheet. For testing API responses, try the API Tester tool. For inspecting responses on the command line, the curl cheat sheet covers the most common flags.