# JSON.jl Float64 serialization (suppress scientific notation)

**URL:** <https://discourse.julialang.org/t/json-jl-float64-serialization-suppress-scientific-notation/119775>\
**Category:** General Usage\
**Tags:** question, json, float, serialization\
**Created:** [September 23, 2024, 9:04pm UTC](https://discourse.julialang.org/t/json-jl-float64-serialization-suppress-scientific-notation/119775 "2024-09-23T21:04:34Z")\
**Posts on this page:** 1\
**Page:** 1

<div class="post-metadata">

**Author:** ![tamasgal](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/tamasgal/32/27946_2.png) [@tamasgal](https://discourse.julialang.org/u/tamasgal)\
**Post date:** [September 23, 2024, 9:04pm UTC](https://discourse.julialang.org/t/json-jl-float64-serialization-suppress-scientific-notation/119775/1 "2024-09-23T21:04:35Z")

</div>

I am having a hard time with JSON.jl. I want to serialize large `Float64` instances without scientific notation and the only way I was able to get at least the rounding working results in a string, instead of a float value 😉

```julia
using Printf
using JSON
import JSON.Serializations: CommonSerialization, StandardSerialization
import JSON.Writer: StructuralContext, show_json

struct RoundedFloatSerialization <: CommonSerialization end

show_json(io::StructuralContext,
            ::RoundedFloatSerialization,
           f::AbstractFloat) =
    show_json(io, StandardSerialization(), @sprintf("%.3f", f))

```

Here is an example which shows that `1e4` is serialized to `10000.0` by default, whereas `1e9` to `1.0e9`. The hook into the `show_json` works, but it yields a `String` for obvious reasons, see below an example.

```julia
julia> JSON.json(1e4)
"10000.0"

julia> JSON.json(1e9)
"1.0e9"

julia> sprint(show_json, RoundedFloatSerialization(), 1e4)
"\"10000.000\""

julia> sprint(show_json, RoundedFloatSerialization(), 1e9)
"\"1000000000.000\""

```

I think I might be on the wrong path and I am pretty sure it’s a fairly common question but wondering at the same time why I don’t find any existing posts about it 😆

Where should I intercept the scientific notation for large floats without being a pirate? 🏴‍☠️

Update: follow-up here [JSON.jl Float64 serialization (suppress scientific notation) · Issue #367 · JuliaIO/JSON.jl · GitHub](https://github.com/JuliaIO/JSON.jl/issues/367)