I recently carved out some time to revisit some dormant projects. The primary driver was a tic-tac-toe app inspired by Scott Wlaschin‘s Enterprise Tic-Tac-Toe series of posts and presentation and a desire to learn and test out Datastar. An upcoming post will dive deeper into that topic. In this post, I want to share a high-level overview of what’s new with FSharp.Data.JsonSchema and Frank. Subsequent posts will dive into further details.

FSharp.Data.JsonSchema 3.0.1

FSharp.Data.JsonSchema is now three packages:

• FSharp.Data.JsonSchema.Core: Core JSON Schema representation types that relies on only FSharp.SystemTextJson. This library can be uses to parse a JSON Schema into F# types and F# types into a JSON Schema. However, it no longer has a specific target.
• FSharp.Data.JsonSchema.NJsonSchema: This is equivalent to the previous version with a dependency on NJsonSchema as the target. This should be backward compatible with previous versions of the library.
• FSharp.Data.JsonSchema.OpenApi: The new target depends on the Microsoft.OpenApi library introduced with the net9.0 framework target. This target is intended for use with generating Open API documents from ASP.NET Core applications.

In addition, several long overdue bug fixes and enhancements should now be resolved:

• Recursive Types (#15): Recursive F# types no longer cause infinite loops. Self-referential DUs, records with optional self-references, and recursion through collections all generate proper $ref: "#" schemas, and a follow-up fix in 3.0.1 resolved an NJsonSchema serialization failure where Ref("#") in nullable contexts tried to look up the root reference in the definitions dictionary instead of referencing the root schema directly
• Choice types (#22): Choice<'A,'B> through Choice<'A,…,'G> now generate clean anyOf schemas instead of the verbose internal-tag encoding
• Anonymous records: Inline object schemas, no $ref
• DU encoding styles: InternalTag, AdjacentTag, ExternalTag, and Untagged via a new unionEncoding parameter on Generator.Create
• Format annotations: Proper date-time, guid, uri, duration, date, time, and byte formats for DateTime, Guid, Uri, TimeSpan, DateOnly, TimeOnly, and byte[]

Frank 7.2.0

Frank has had a long and winding history as my favorite hobby project for trying out different approaches to encoding web applications. The computation expression approach starting in (IIRC) v5.0 has stuck. The goal is still to produce an HTTP resource-style set of builders that provides a consistent means of defining HTTP resources and the ASP.NET Core WebHost in which to run them while allowing for a lot of flexibility and extensibility. As such, I’ve added some additional libraries I’ve found useful to test out the extensibility and support the new tic-tac-toe hobby project mentioned above.

Packages

• Frank: Added Metadata field to ResourceSpec, a list of (EndpointBuilder -> unit) convention functions applied during RouteEndpointBuilder.Build(). This generic extensibility point lets companion libraries (Auth, OpenApi, etc.) attach typed endpoint metadata without requiring changes to the core Frank library. This is a binary-breaking change but source-compatible with the empty default. Also added plugBeforeRouting, plugBeforeRoutingWhen, and plugBeforeRoutingWhenNot for middleware ordering control around UseRouting().
• Frank.Analyzers: F# Analyzer (FSharp.Analyzers.SDK) that detects duplicate HTTP handler registrations within a resource block at compile time, enforcing the constraint of a single HTTP method per resource. It works in IDEs (Ionide, VS, Rider) and CLI (dotnet fsharp-analyzers) for CI/CD.
• Frank.Auth: Adds WebHostBuilder registration and resource-level authorization via ResourceBuilder extensions, including requireAuth, requireClaim, requireRole, requirePolicy using AND semantics for resources and useAuthentication, useAuthorization, authorizationPolicy for WebHostBuilder.
• Frank.OpenApi: Adds long-planned, declarative OpenAPI 3.0+ document generation, including a handler computation expression for pairing handlers with metadata (name, summary, tags, produces, accepts). F# type schemas (records, DUs, options, collections) via FSharp.Data.JsonSchema.OpenApi. useOpenApi on WebHostBuilder wires services and middleware. Includes Scalar UI to provide a web-based client for viewing and testing endpoints. Targets net9.0/net10.0.
• Frank.Datastar: Native SSE implementation similar to the StarFederation.Datastar.FSharp library. Zero-copy buffer writing via IBufferWriter, zero external NuGet dependencies, full Datastar SDK ADR compliance. Added stream-based overloads (streamPatchElements, etc.) accepting TextWriter -> Task for zero-allocation HTML rendering. No breaking API changes. Targets net8.0/net9.0/net10.0.

New Samples

• Frank.Datastar.Basic: RESTful hypermedia patterns (click-to-edit, search, bulk ops) using Frank.Datastar with F# string templates.
• Frank.Datastar.Hox: Same patterns as Basic using the Hox view engine. Demonstrates stream-based SSE overloads via Render.toStream.
• Frank.Datastar.Oxpecker: Same patterns as Basic using Oxpecker.ViewEngine.
• Frank.OpenApi.Sample: Product catalog API demonstrating the handler CE with OpenAPI metadata, mixed plain/enriched handlers, useOpenApi, and Scalar UI.

Looking Ahead

I’ll spend some time in upcoming posts exploring each of these. In the meantime, I’d love feedback on any of the updates and changes. I hope I haven’t broken anyone with changes to FSharp.Data.JsonSchema, and there is a transition package with version 3.0.0 to make it easier to switch without changing package names. I don’t have any additional plans at the moment for either of these, but please open issues if you have ideas or bug reports.