How is JSON encoded in the generated JavaScript?

Toolpaper detects Content-Type: application/json and emits idiomatic fetch JSON serialization (json= for requests, Response.json for Go, etc.).

Does it preserve Content-Type?

Yes. The Content-Type header is honored and matched against the body so serialization stays consistent.

Is anything uploaded?

No. Parsing and generation happen entirely in your browser.

Send JSON with cURL in JavaScript

Paste a curl command that sends JSON and get idiomatic JavaScript code. We pick the right serialization for fetch and set the correct Content-Type.

Quick answer

To convert a cURL command to JavaScript, paste it into the Toolpaper workbench below. It parses the command in your browser and emits idiomatic JavaScript code — headers, query string, request body, authentication (Bearer, Basic, API key), and cookies are all wired up automatically. No data is uploaded; conversion is fully client-side.

Prefer a different target? See the full cURL to JavaScript reference, or jump to the same guide in Node.js, Python, or Go.

InputcURL command

MethodPOST·Headers1·Body40 B· Chars 132

OutputJavaScript · fetch(browser/Node)

const response = await fetch("https://api.example.com/users", {
  method: "POST",
  headers: {
    "Content-Type": "application/json"
  },
  body: "{\"name\":\"Ada\",\"email\":\"ada@example.com\"}",
  redirect: "manual"
});
const data = await response.json();

Inspect

Example

A representative curl command for this scenario. Paste your own above to convert an exact match.

curl input

curl -X POST https://api.example.com/users \
  -H "Content-Type: application/json" \
  -d '{"name":"Ada","email":"ada@example.com"}'

Implementation notes

Content-Type is detected from -H headers first, then inferred from the body shape when the header is missing.
JSON bodies are parsed and re-emitted through fetch's serializer so quoting stays consistent with what the server expects.
Charset directives on Content-Type (e.g. application/json; charset=utf-8) survive the round trip.

Common mistakes

Setting Content-Type manually and then also using fetch's helper — you end up with duplicate headers or the wrong one wins.
Mixing form encoding with JSON headers — the server rejects with 400 and it's easy to miss in code review.
Trusting the browser DevTools "Copy as cURL" to preserve charset — it often drops it. Clean panel restores common defaults.

Common questions

How is JSON encoded in the generated JavaScript?: Toolpaper detects Content-Type: application/json and emits idiomatic fetch JSON serialization (json= for requests, Response.json for Go, etc.).
Does it preserve Content-Type?: Yes. The Content-Type header is honored and matched against the body so serialization stays consistent.
Is anything uploaded?: No. Parsing and generation happen entirely in your browser.

More payload types in JavaScript

JavaScript hub →

form-urlencoded in JavaScript

/how-to/send-form-with-curl-in-javascript

multipart form-data in JavaScript

/how-to/send-multipart-with-curl-in-javascript

XML in JavaScript

/how-to/send-xml-with-curl-in-javascript

GraphQL in JavaScript

/how-to/send-graphql-with-curl-in-javascript

The same guide in other languages

All guides →

In Node.js

/how-to/send-json-with-curl-in-node

In Python

/how-to/send-json-with-curl-in-python

In Go

/how-to/send-json-with-curl-in-go

In PHP

/how-to/send-json-with-curl-in-php

In Ruby

/how-to/send-json-with-curl-in-ruby

In Rust

/how-to/send-json-with-curl-in-rust

In Java

/how-to/send-json-with-curl-in-java

In Kotlin

/how-to/send-json-with-curl-in-kotlin

Full JavaScript reference on the cURL to JavaScript hub, or open the main converter for all 18 targets.