Message-format converter
Paste a conversation in OpenAI, Anthropic or Gemini shape and get it back in another. Every construct that could not be carried across is named rather than dropped.
Your input is processed in this browser. It is not uploaded. A file or pasted rows go nowhere. A URL is fetched by your browser directly from the address you give it. Sharing creates a link containing the data you choose to include.
This link will contain
Anyone with the link can read this. Compression is not encryption.
What it does
The three big APIs shape a conversation differently: where the system prompt lives, how a tool call is paired to its result, whether content is a string or a list of blocks. Moving a conversation between them by hand is where the subtle bugs come from: a tool result that no longer answers anything, a system prompt that quietly became a user turn.
This converter goes through one canonical form, so any direction works, and anything with no equivalent in the target is listed under Notes and assumptions rather than silently dropped. Read that list before you trust the output.
What it does not do
It does not know vendor extension fields, and it does not guess. An unknown part type is a note and a gap, not a pass-through the target will reject.