Fsharp

What it does

When your agent uses it

• : F .fs/.fsproj code
• Discriminated unions
• Pattern matching
• Computation expressions

Example prompts

• “/fsharp”

Requirements

• Compatibility (from SKILL.md): Requires a .NET SDK with F# support and an F# project, script, or interop boundary.

Workflow steps

5 steps, taken from the first numbered list in SKILL.md.

1. 1Inspect the existing .fsproj, .fs, .fsi, and .fsx files to determine compile order, public boundaries, and whether the code is F#-first or…
2. 2Choose the smallest F# model that represents the invariant: records for named product data, discriminated unions for closed state, option…
3. 3Add or edit source files in dependency order, then update the .fsproj compile list before consumers reference the new code.
4. 4Review public API shape for .NET interop. Translate F#-specific internal models to DTOs, methods, or Try* patterns when C# callers need a…
5. 5Run dotnet build, targeted tests, and any relevant dotnet fsi probes before returning the final result.

What it can do on your machine

Read from SKILL.md and the folder at commit 535dd55. It shows what the files ask for, not the result of running them.

• Tool permissions

  Pre-approves nothing: there is no allowed-tools line, so your agent's usual permission prompts apply.

  From allowed-tools in the SKILL.md frontmatter.

• Runs code

  Shell commands in SKILL.md call:

  • dotnet

  From the folder's file list and the shell code blocks in SKILL.md.

• Network

  Links to these hosts (documentation or services it may open):

  • learn.microsoft.com

  From URLs in SKILL.md, links to its own repository left out.

• Credentials

  Names no API keys, tokens, secrets or passwords.

  From names ending in _API_KEY, _TOKEN, _SECRET, _KEY or _PASSWORD in SKILL.md.

• Compatibility

  Requires a .NET SDK with F# support and an F# project, script, or interop boundary.

  From compatibility in the SKILL.md frontmatter.

Context cost

Fsharp loads about 1.9k tokens when it runs. Until then it costs about 164 tokens; SKILL.md has 605 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it

~164

When it runs · the whole SKILL.md, loaded when a task matches

~1.9k

Estimates: characters ÷ 4, the usual rule of thumb; real counts depend on the model's tokenizer. Scripts and assets cost tokens only if the agent reads them.

Safety

Automated static check — not a guarantee. Review scripts before installing. It scans the text of SKILL.md for risky patterns (piping downloads into a shell, reading credential files, hidden Unicode, destructive commands); files beside SKILL.md are not scanned.

SKILL.md

The full file from managedcode/dotnet-skills at commit 535dd55, republished under its MIT licence (© managedcode). 605 words, ~1,935 tokens.

name

fsharp

description

Write, review, or modernize F# code in .NET repositories with functional-first design, algebraic data types, pattern matching, pipelines, async workflows, project ordering, and C# interop. USE FOR: F# .fs/.fsproj code; discriminated unions, records, options, results, pattern matching, computation expressions, or functional domain modeling; strongly typed AI-generated .NET code. DO NOT USE FOR: C# language modernization; FSI-only exploratory scripts with no project changes. INVOKES: inspect .fsproj file order and SDK settings, edit F# source and project files, and run dotnet build/test or dotnet fsi validation commands when changes are made.

compatibility

Requires a .NET SDK with F# support and an F# project, script, or interop boundary.

dotnet new classlib -lang "F#" -o src/Domain
dotnet new console -lang "F#" -o src/App
dotnet new xunit -lang "F#" -o tests/Domain.Tests
dotnet sln add src/Domain/Domain.fsproj tests/Domain.Tests/Domain.Tests.fsproj
dotnet add tests/Domain.Tests/Domain.Tests.fsproj reference src/Domain/Domain.fsproj
dotnet build

dotnet add src/Domain/Domain.fsproj package FSharp.Core

<ItemGroup>
  <Compile Include="Domain.fs" />
  <Compile Include="Validation.fs" />
  <Compile Include="Program.fs" />
</ItemGroup>

module Orders

type OrderId = private OrderId of string

module OrderId =
    let tryCreate value =
        if System.String.IsNullOrWhiteSpace value then
            Error "Order id is required."
        else
            Ok (OrderId value)

type Payment =
    | Card of last4: string
    | Wire of iban: string
    | PurchaseOrder of number: string

type Order =
    { Id: OrderId
      Customer: string
      Payment: Payment }

let describePayment payment =
    match payment with
    | Card last4 -> $"card ending {last4}"
    | Wire iban -> $"wire transfer {iban}"
    | PurchaseOrder number -> $"purchase order {number}"

module Pricing

type Price =
    private
    | Price of decimal

module Price =
    let tryCreate amount =
        if amount < 0m then
            Error "Price cannot be negative."
        else
            Ok (Price amount)

    let value (Price amount) = amount

type Line =
    { Sku: string
      Quantity: int
      UnitPrice: Price }

let tryCreateLine sku quantity amount =
    match Price.tryCreate amount with
    | Ok price when quantity > 0 ->
        Ok { Sku = sku; Quantity = quantity; UnitPrice = price }
    | Ok _ ->
        Error "Quantity must be positive."
    | Error message ->
        Error message

open System.IO

let readActiveUsers path =
    File.ReadLines path
    |> Seq.skip 1
    |> Seq.choose (fun line ->
        match line.Split(',') with
        | [| id; name; "active" |] -> Some {| Id = id; Name = name |}
        | _ -> None)
    |> Seq.toList

namespace Company.Domain

type InvoiceDto =
    { Id: string
      Total: decimal
      IsPaid: bool }

module Invoice =
    let markPaid invoice =
        { invoice with IsPaid = true }

dotnet build
dotnet test
dotnet fsi scripts/check.fsx

© managedcode, MIT. Rendered from Markdown: HTML in the file is shown as text, images as links, and headings moved down two levels. Raw file

Files

SKILL.md and 1 other file in catalog/Tools/FSharp/skills/fsharp of managedcode/dotnet-skills.

• SKILL.md
• manifest.json

Open the folder on GitHubat commit 535dd55