Names

Container and resource names follow the same rules on every provider:

• Case-sensitive. Report.pdf and report.pdf are different resources, and Docs and docs are different containers, whatever the SQL Server's collation.
• Length: a container name has 1 to 128 characters (ResourceNames.MaxContainerNameLength), and a resource name 1 to 256 (ResourceNames.MaxResourceNameLength).
• No whitespace at either end. SQL Server ignores trailing spaces when it compares strings, so names that differ only there are rejected rather than treated as the same name.
• No control characters, bidirectional controls or unpaired surrogates 4.0. Control characters, such as line breaks and tabs, break headers and logs. Unicode's bidirectional controls (U+061C, U+200E and U+200F, U+202A to U+202E, and U+2066 to U+2069) can make a name display as another: a name made of invoice, U+202E and fdp.exe shows as invoiceexe.pdf. An unpaired surrogate isn't valid text, so JSON and HTTP replace it, and an export would change the name.

Any other character is allowed, including /, so 2026/10/report.pdf is a valid resource name. Containers don't nest, though: the slash is just part of the name. Joiners (U+200C and U+200D), which some scripts and emoji need, are allowed too.

The rule on these characters applies only to names a write creates: uploads, the names copies, moves and renames go to, and containers being created or imported. A name stored by 3.1 or earlier, which allowed these characters, can still be read and deleted, and an export of it can be imported; a resource with one can be moved or renamed to a name that follows the rule. CreateContainerIfNotExistsAsync still finds a container with such a name, and checks the rule only when it creates one.

Every method that takes a name checks it before contacting storage, and throws ArgumentNullException for null and ArgumentException for a name that breaks the rules, so an API can turn that into a 400. To check a name yourself first, for example to validate a whole request before acting on any of it, call ResourceNames.IsValidContainerName or ResourceNames.IsValidResourceName.

Names appear in URIs and file names that you build from them, so escape them there; see URI providers and ASP.NET Core.