Limitations

The library implements the protocol of SQL Server, not a database. This page lists what it does not do.

General

Needs the ASP.NET Core shared framework.
The query engine needs reflection: the package is trimmable and compatible with Native AOT, but the query engine is not. See Trimming and Native AOT.
No database: the server stores nothing and runs no SQL by itself. Your query handler, or the query engine, answers every request.

SQL batches, RPC calls, bulk loads and local transactions only. Other request types return the error 50001 "Unsupported packet type".
No distributed transactions (System.Transactions, MSDTC): their requests return the error 50001. See Transactions.
Bulk loads are received batch by batch: a batch of SqlBulkCopy cannot be larger than MaxMessageSize, and decimal columns are declared decimal(38, 10). See Bulk loads.
Text columns use one collation. Variant, UserDefined and Table columns are sent as nvarchar text.

No Microsoft Entra ID authentication. SQL logins and integrated Windows authentication (NTLM, Kerberos, through an SSPI exchange run by the authentication handler) are supported. See Authentication.
TLS 1.2 when TLS is negotiated in the TDS PRELOGIN exchange (Encrypt=True or Optional). Use Encrypt=Strict for TLS 1.3. See Encryption.
No encryption by default: without a certificate, passwords and data travel in clear text.

SELECT statements only: no recursive common table expressions, no INSERT, UPDATE or DELETE. See Supported SQL.
LIKE compares characters ordinally, so it is case-sensitive.
The XML methods take XPath 1.0, not XQuery.
A stored procedure that returns an IQueryable is enumerated synchronously.