Chiron 7 vs Newtonsoft, from https://github.com/haf/chiron/commit/075e1ad611d6f1b20f161057afe94d5d7376ce03 on netcoreapp2.0

command.sh

dotnet build -c Release benchmarks/Chiron.Benchmarks/Chiron.Benchmarks.fsproj && \
    dotnet benchmarks/Chiron.Benchmarks/bin/Release/netcoreapp2.0/Chiron.Benchmarks.dll --class ParseTest

gistfile1.txt

// * Summary *

BenchmarkDotNet=v0.10.14, OS=macOS High Sierra 10.13.5 (17F77) [Darwin 17.6.0]
Intel Core i7-7920HQ CPU 3.10GHz (Kaby Lake), 1 CPU, 8 logical and 4 physical cores
.NET Core SDK=2.1.200
  [Host]    : .NET Core 2.0.7 (CoreCLR 4.6.0.0, CoreFX 4.6.26403.03), 64bit RyuJIT
  MediumRun : .NET Core 2.0.7 (CoreCLR 4.6.0.0, CoreFX 4.6.26403.03), 64bit RyuJIT

Job=MediumRun  LaunchCount=2  TargetCount=15
WarmupCount=10

     Method |       Name |           Mean |       Error |        StdDev |     Gen 0 |     Gen 1 |    Gen 2 |  Allocated |
----------- |----------- |---------------:|------------:|--------------:|----------:|----------:|---------:|-----------:|
 Chiron_New |      error |       3.423 us |   0.0672 us |     0.0963 us |    0.2823 |         - |        - |     1200 B |
 Newtonsoft |      error |       1.926 us |   0.1739 us |     0.2380 us |    1.6289 |         - |        - |     6840 B |
 Chiron_New |    fparsec |      19.657 us |   0.2533 us |     0.3551 us |    1.4648 |         - |        - |     6200 B |
 Newtonsoft |    fparsec |       9.459 us |   0.0957 us |     0.1432 us |    3.2349 |         - |        - |    13576 B |
 Chiron_New | prettyuser |      48.209 us |   0.7862 us |     1.1768 us |    3.9063 |         - |        - |    16632 B |
 Newtonsoft | prettyuser |      20.805 us |   0.1651 us |     0.2259 us |    5.4626 |         - |        - |    22968 B |
 Chiron_New |     social | 125,279.691 us | 825.6099 us | 1,210.1683 us | 5812.5000 | 1937.5000 | 625.0000 | 30154333 B |
 Newtonsoft |     social |             NA |          NA |            NA |       N/A |       N/A |      N/A |        N/A |
 Chiron_New |       user |      45.557 us |   0.4152 us |     0.6085 us |    3.9063 |         - |        - |    16632 B |
 Newtonsoft |       user |      20.237 us |   0.2521 us |     0.3695 us |    5.4626 |         - |        - |    22968 B |

Benchmarks with issues:
  ParseTest.Newtonsoft: MediumRun(LaunchCount=2, TargetCount=15, WarmupCount=10) [Name=social]

ParsingAndFormatting.fs

namespace ChironB.Benchmarks

open Chiron
open BenchmarkDotNet.Attributes
open Newtonsoft.Json
open Newtonsoft.Json.Linq

module Bench =
    open System.IO
    open System.Text

    let resetStream (stream : #Stream) =
        stream.Seek(0L, SeekOrigin.Begin) |> ignore

    module Chiron =
        let inline parse (stream: #Stream): Json =
            let reader = new StreamReader(stream)
            reader.ReadToEnd()
            |> Json.parse
            |> JsonResult.getOrThrow

        // let inline parseAndDeserialize (stream : #Stream) : 'a =
        //     let reader = new StreamReader(stream)
        //     reader.ReadToEnd()
        //     |> Json.parse
        //     |> Json.deserialize

    module JsonNET =
        let serializer = JsonSerializer.CreateDefault()

        let inline parse (stream: #Stream): JObject =
            let jsonReader = new StreamReader(stream, Encoding.UTF8)
            let reader = new JsonTextReader(jsonReader, CloseInput = false)
            JObject.Load reader

[<Config(typeof<CoreConfig>)>]
type ParseTest () =
    let mutable jsonStream = null
    let mutable jsonString = null

    [<Setup>]
    member this.Setup () =
        jsonString <- loadJsonResourceAsString this.Name
        jsonStream <- loadJsonResource this.Name

    [<Params("error", "fparsec", "user", "prettyuser", "social")>]
    member val Name = "<null>" with get, set

    [<Benchmark>]
    member __.Chiron_New (): Chiron.JsonResult<Chiron.Json> =
        Chiron.Parsing.Json.parse jsonString

    [<Benchmark>]
    member __.Newtonsoft () =
        Bench.resetStream jsonStream
        Bench.JsonNET.parse jsonStream

[<Config(typeof<CoreConfig>)>]
type FormatTest () =
    let mutable jsonN = Chiron.Json.Null

    [<Setup>]
    member this.Setup () =
        jsonN <-
            loadJsonResourceAsString this.Name
            |> Chiron.Parsing.Json.parse
            |> Chiron.JsonResult.getOrThrow

    [<Params("error", "fparsec", "user", "prettyuser", "social")>]
    member val Name = "<null>" with get, set

    [<Benchmark>]
    member __.Chiron_New () =
        Chiron.Formatting.Json.format jsonN

[<Config(typeof<CoreConfig>)>]
type FormatVariableLengthStrings () =
    let mutable simpleJson = Chiron.Json.Null
    let mutable escapedJson = Chiron.Json.Null

    [<Params(10, 100, 1000, 10000, 100000)>]
    member val public strlen = 1 with get, set

    [<Setup>]
    member x.Setup () =
        let simple = String.replicate x.strlen "a"
        simpleJson <- Chiron.Json.String simple
        let escaped = String.replicate (x.strlen / 10) "\\u0004\\n\\\""
        escapedJson <- Chiron.Json.String escaped

    [<Benchmark>]
    member __.Simple_New () =
        Chiron.Formatting.Json.format simpleJson

    [<Benchmark>]
    member __.Escaped_New () =
        Chiron.Formatting.Json.format escapedJson

You can get the best of both worlds by using Fleece which supports NewtonSoft as Json encoder/decoder.

Actually Fleece is the original F# project (the original is Haskell's AESON) while Chiron seems to be a bad copy of Fleece, which implements its own parsers (a bad idea).

Looks like the performance of Newtonsoft is heavily dependant on where it runs. There are multiple compilation flags. For instance some IL-emit code is not done in netcore, while it's done for some versions of net\d+