This might be a possible duplicate with this.
I want to know a proper way to insert additional string with OP_RETURN and retrieve the transaction from block chain and decode it accordingly.
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Essentially, one of the output scripts should be
OP_RETURN <the data you want to add>
Let me give an example. Say you want to add the string "Melons." to the blockchain.
That's... trickier. Bitcoin is not optimized for searching the metadata of transactions.