What actually differs between the two formats?

ChatGPT puts the system instruction inside the messages array as a system role. Claude takes a separate top-level system parameter and uses a Human/Assistant turn structure. The content is the same; only the envelope differs.

Does converting change my prompt's meaning?

No. The converter only re-shapes the structure — it moves the system instruction and re-labels turns. Your wording and intent are preserved exactly.

How do I label my input?

Prefix lines with System:, User:, or Human:. Everything under System becomes the system instruction; everything under User or Human becomes the message body. Unlabeled text is treated as the user message.

Does it need an API key?

No. Conversion happens entirely in your browser with no network call. Paste in, copy out — nothing is sent anywhere.

Why does Claude output show a system comment instead of JSON?

Claude's system instruction is passed as a separate API parameter, not inside the message array. The output marks it clearly so you know to set it as the top-level system field rather than as a turn.

ChatGPT vs Claude Prompt Formatter

ChatGPT vs Claude prompt formatter

ChatGPT and Claude accept the same ideas but expect different envelopes. GPT wants a messages array with a system role inside it; Claude wants a separate top-level system parameter and Human/Assistant turns. Copying a prompt straight from one to the other usually means hand-editing the structure. The ChatGPT vs Claude prompt formatter does that conversion in one click while preserving your wording.

How it works

You tell the tool which format your prompt is in and paste it using System:, User:, or Human: labels. Converting GPT → Claude pulls the system instruction out into Claude’s top-level system field and rebuilds the body as a Human turn. Converting Claude → GPT folds the leading system paragraph back into a system message and emits valid OpenAI-style JSON. Only the envelope changes — your intent, constraints, and examples stay intact. Everything runs locally with no API key and no network call.

Tips and notes

Label your input clearly. A System: line tells the tool what belongs in the system slot; without it, everything becomes the user message.
Set Claude’s system separately. The Claude output flags the system text as a parameter — pass it as the top-level system field, not as a turn.
Wrap pasted documents in tags. Claude responds well to XML-style tags around long inputs; add them around any article or data you embed.
Round-trip to sanity-check. Convert one way then back to confirm no part of the prompt was dropped before you commit to a provider.