Curl → Fetch Converter
Translate curl commands into JavaScript fetch requests.
Curl → Fetch Converter
Runs entirely in your browser
This tool executes locally using standard browser APIs (for example window.crypto.getRandomValues or crypto.subtle where applicable). Your input is not transmitted to or stored on a ScriptPulse server. See How Calculations Work.
What This Tool Does
- The Curl → Fetch Converter translates an existing curl command into equivalent JavaScript using the Fetch API — the request you already have, copied from documentation, a bug report, or your own terminal history, converted into code you can paste directly into a browser or Node.js script rather than hand-translating each flag yourself.
- This translation is mechanical but easy to get subtly wrong by hand: curl's -X, -H, and -d flags each map to a specific part of fetch's options object (method, headers, body), but body values need to go from curl's shell-quoted string to a JSON.stringify() call, and headers need to become a proper object rather than a repeated flag — small details that are exactly the kind of thing worth automating rather than re-deriving under time pressure.
How It Works
- The curl command's method is detected — a POST is inferred either from an explicit -X POST flag or the presence of a -d data flag, since curl defaults to GET otherwise.
- The target URL is extracted from the command's quoted argument.
- Any -d payload is extracted and will be wrapped in a JSON.stringify() call in the generated fetch body, assuming a JSON payload (the common case for modern APIs).
- A Content-Type: application/json header is added to the generated headers object when the original curl command's body or headers indicate JSON, producing a complete fetch() call with method, headers, and body assembled correctly.
Usage
- Paste the curl command you want to convert.
- Run the conversion.
- Copy the generated fetch() call.
- Adjust the generated code as needed — for example, adding error handling or additional headers the automatic conversion didn't fully capture.
Examples
- Converting a curl command that posts a JSON payload into a fetch call, to paste directly into a frontend form-submission handler.
- Converting a curl command found in third-party API documentation into fetch code as the starting point for a new integration.
- Converting a curl command from a bug report to reproduce a failing request directly in the browser's developer console for debugging.
- Comparing the generated fetch code against a hand-written version to check whether a header or body detail was missed during a manual translation attempt.
Real-World Use Cases
- Converting a curl command copied from API documentation directly into fetch code for a frontend or Node.js integration, without hand-translating flags and quoting.
- Turning a curl command from a colleague's bug report into runnable JavaScript to reproduce and debug the issue directly in your own code.
- Quickly prototyping a fetch call against an endpoint you've already tested and confirmed works via curl, skipping the manual translation step.
- Learning how curl's flags map to fetch's options object, by converting a few different sample commands and comparing input to output.
Best Practices
- Always review the generated fetch code before using it in production — automatic conversion handles the common cases well but may not capture every flag from an unusually complex curl command.
- Add response error handling (checking response.ok, catching network failures) to the generated code — curl's own error reporting doesn't map directly to fetch's promise-based model, and the conversion focuses on request construction, not response handling.
- Double-check that a Content-Type header genuinely matches the body you're sending — if the original curl command's body wasn't actually JSON, forcing a JSON.stringify() call in the generated code will produce an incorrect request.
- Treat any credential present in the original curl command with the same caution in the generated code — converting formats doesn't reduce the sensitivity of an embedded token or key.
Common Mistakes
- Assuming the generated fetch call handles the HTTP response the same way curl's terminal output does — fetch requires an explicit .then(response => response.json()) (or similar) step that curl doesn't need, since curl prints the raw response by default.
- Not noticing that a curl command's implicit defaults (such as automatically following redirects) aren't automatically replicated by a bare fetch() call, which requires its own redirect handling if that behavior matters.
- Converting a curl command with a non-JSON body (like form-encoded data) and ending up with an incorrect JSON.stringify() wrapper, since the conversion's common-case assumption is a JSON payload.
- Pasting a curl command containing a real credential into any browser tool without treating that credential as compromised afterward.
Limitations
- This tool handles the common case of a JSON-bodied request with a single header well; curl commands using multiple headers, file uploads, or non-JSON bodies may need manual adjustment after conversion.
- It does not execute the generated fetch call or verify it actually works against the real endpoint — review and test the output in your own environment.
- Complex curl flags beyond method, URL, a single header, and a data payload (cookies, client certificates, proxy settings, and similar) are not translated automatically.
Technical Reference Guide
- The Fetch API this tool generates code for is a WHATWG Living Standard, not an IETF RFC, maintained collaboratively by browser vendors.
- The underlying HTTP semantics both curl and fetch ultimately express (methods, headers, request bodies) are defined by RFC 9110.
- JSON request bodies, the common case this converter assumes, follow the grammar defined in RFC 8259.
Specifications & Standards
FAQ
Why does the generated code need an extra .then() step that curl didn't need?
curl prints a response's raw body directly to your terminal by default. fetch instead returns a Promise that resolves to a Response object — you need an explicit step (like response.json()) to actually read the body content.
Will this handle a curl command with multiple headers?
The converter handles a single header cleanly; for multiple headers, add the additional key-value pairs to the generated headers object yourself, following the same pattern as the one the tool produced.
What if my curl command's body isn't JSON?
The conversion assumes a JSON payload, the common case for modern APIs. If your body is form-encoded or another format, you'll need to adjust the generated code's body construction (and Content-Type header) to match your actual payload type.
Does the generated fetch call include error handling?
Not automatically — add your own .catch() or try/catch around the fetch call, and check response.ok before assuming a non-network-level failure (like a 404 or 500) succeeded, since fetch doesn't reject its promise for HTTP error status codes by default.
What's the difference between this tool and the Curl → Python Requests Converter?
Same source input (a curl command), different target language — this tool produces JavaScript fetch code, the other produces Python using the requests library. Use whichever matches the environment you're actually writing code for.
Is it safe to convert a curl command containing an API key?
Treat it the same as pasting the key into any other tool — no longer fully confidential. Use a test credential where possible, and rotate any real key that's been entered anywhere outside your own trusted systems.
Part of this Developer Hub
This utility is part of our comprehensive API & Web Engineering topic workspace.
Explore foundational guidelines, technical specifications, and other interactive utilities related to this workflow.
Related Tools
Explore related utilities inside the API & Web Engineering Lab workshop for complementary engineering workflows.
View all API & Web Engineering Lab tools