The first time I got a confirmed transaction on devnet, I felt great for about 10 seconds.
Then I thought: I have no idea what actually just happened.
I'd been treating transactions like a black box. Type address, type amount, hit send, done. But that stops working the moment something breaks — or the moment you try to build anything beyond a basic transfer.
So I went and figured it out. Turns out a Solana transaction is made of four things. Once you see what each one does, a lot of other stuff clicks into place.
The four parts
- Instructions — what you want to do
- Accounts — what data will be touched
- Signatures — proof of authorization
- Recent blockhash — a built-in expiry stamp
That's it. Let's go through them.
Instructions
An instruction is the action. It says: call this program, with these inputs.
For a basic SOL transfer, the instruction calls Solana's System Program — a built-in program that handles things like moving SOL between wallets. You don't deploy it, it's just there.
The thing that surprised me: one transaction can hold multiple instructions. You could transfer SOL, create an account, and call another program — all in one shot. And it's all-or-nothing. Either every instruction succeeds or the whole transaction fails. No partial results.
Accounts
In Solana, almost everything is an account — your wallet, a token balance, a deployed program. The whole network state is basically one giant table where every row has an address and some data.
When you write an instruction, you have to declare every account it will touch upfront — even ones you're only reading. You also mark each one as writable or read-only, and whether it needs to sign.
This felt like extra work at first. But the reason is smart: Solana uses that list to figure out which transactions can run in parallel. No shared accounts = no conflict = process them at the same time. It's a big part of why Solana can handle so many transactions per second.
The recent blockhash
Every transaction has to include a recent blockhash — a hash of a block that was produced recently on the chain.
It does two things.
First, replay protection. Without it, someone could take your signed transaction and submit it again later. The blockhash ties the transaction to a specific moment, so the network rejects anything that references an old one.
Second, expiry. A blockhash is only valid for about 150 blocks — roughly 60 to 90 seconds. After that window, the transaction is dead. You'd need a fresh blockhash and start over.
This is where Solana diverges from anything in Web2. A database transaction doesn't expire. You can open one, walk away, come back. Solana transactions are more like a signed cheque with an expiry date on it — legitimate signature, but useless after the window closes.
Practical note: fetch the blockhash as late as possible, right before you send.
Signatures
Before a transaction is broadcast, it gets signed with your private key. Validators verify the signature against your public key before running anything.
If the transaction was tampered with after signing, the signature won't match and it gets rejected.
Two things worth knowing:
Transactions can need multiple signatures. Some programs require both parties to sign. Multisig setups require a minimum number of co-signers.
The signature is the transaction ID. That long string in the Explorer URL? That's not a separately generated ID — it's the actual cryptographic signature. Every transaction ID on Solana is its own proof of authorization.
Go look at one on Explorer
Open any of your devnet transactions on Solana Explorer. You'll see:
- Account Inputs — every account, labeled writable or read-only
- Instructions — each one expanded with its program and data
- Signatures — at the bottom of the page
Map what you see back to the four parts above. It lands differently when the transaction on screen is one you sent yourself.
The one thing to take away
A Solana transaction isn't just a request. It's a signed, time-limited, all-or-nothing bundle that declares its own authorization and expiry before it hits the network.
Once that settled in for me, a lot of things that seemed weird about Solana started making sense.
Part of my #100DaysOfSolana journey.