Transaction Broadcast · SolanaLand fast.
Earn the spread.
Fast lands your transaction in the slot that is already open, 0-slot delay, then monetizes it: the arbitrage your own trade leaks is captured, and 65% of that value goes straight to your cashback address, in SOL.
"cashbackAddress": "YourSolanaAddress"65% backcurrent slot
298 472 841
next slot
298 472 842
How it worksSubmit to confirmed, same slot. Paid back too.
Submit your raw transaction
Send your Base58 or Base64 encoded transaction to fast.circular.fi/transactions via a standard JSON-RPC POST. Include your API key in the x-api-key header.
Instant network propagation
Fast pushes your transaction through the broadest possible set of nodes simultaneously. The goal is simple: reach as many validators as possible before the current slot boundary, 200ms wide, closes.
Land in the current slot
Your transaction lands in the slot that's already open, not the next one 200ms later. For snipers, liquidators, and time-sensitive strategies, that single slot is the difference between winning and missing.
Get paid for the value you moved
Your trade shifts prices and leaks value to arbitrageurs. Fast captures that arbitrage on the same transaction and sends 65% of it in SOL to the cashbackAddress you passed in, automatically, no extra call.
CashbackYour transaction leaks value. 65% comes back to you.
Every swap you send moves a pool and creates an arbitrage worth real SOL. Today that value goes to whoever backruns you. With Fast it is captured on your own transaction and the majority is returned to your cashback address.
arbitrage captured on your transaction
Sent to cashbackAddress
In SOL, on every broadcast
Execution and validator costs
What keeps the routing running
Where the spread goes
A searcher backruns your trade and keeps 100% of the spread. You paid the price impact, they took the profit.
Fast lands you 0-slot and captures that same spread, then routes 65% back to your address. Your transaction pays for itself.
Paid in SOL, to your address
Add one cashbackAddress field to your request. Fast credits the SOL there, no claim flow, no separate contract to call.
Your leak, not someone else's
The value comes from the price impact of your own transaction. Fast backruns it in the same slot instead of leaving it to third-party searchers.
Speed stays the priority
Monetization never delays the broadcast. The transaction goes out 0-slot first, the arbitrage is captured around it.
FeaturesBuilt for 0-slot landing.Every landed transaction also pays you back 65% of the arbitrage it leaks.
Current slot, not next
Solana slots are 200ms long, and most transactions miss the one they were sent for. Fast reaches validators before the boundary closes, so your transaction lands in the open slot instead of queueing for the next.
Lands in current slot
0-slot delay
Queued for next slot
~200ms behind
65% cashback, one field
The arbitrage your transaction leaks is captured and mostly returned to you.
cashbackAddress65% IN SOLomittedNO CASHBACKGlobal infrastructure
Nodes distributed worldwide minimize the physical distance between your request and the nearest validator. Every millisecond counts.
Drop-in JSON-RPC
Same sendTransaction format as any Solana RPC. Swap the URL, add your API key header. Nothing else changes in your code.
Base58 or Base64
Send your transaction in either encoding. No serialization changes needed, whatever your wallet or SDK already produces.
One endpoint.
Up and running in minutes.
Fast uses the standard JSON-RPC sendTransaction format. If you already talk to a Solana RPC, switching to Fast is a one-line change.
POST fast.circular.fi/transactionsx-api-key headerJSON-RPC 2.0 · sendTransactioncurl -X POST https://fast.circular.fi/transactions \
-H "Content-Type: application/json" \
-H "x-api-key: YOUR_API_KEY" \
-d '{
"jsonrpc": "2.0",
"id": 1,
"method": "sendTransaction",
"params": [
"<BASE58_OR_BASE64_TX>",
{
"cashbackAddress": "YourSolanaAddress"
}
]
}'
HTTPS or gRPC. Your stack, your call.
Both transports hit the same infrastructure. Same 0-slot landing, same 65% cashback, pick whatever fits your stack.
HTTPS · JSON-RPC 2.0
Drop-in Solana compatible
Endpoint
POST fast.circular.fi/transactionsAuth
x-api-key headerEncoding
Base58 or Base64Format
JSON-RPC 2.0 · sendTransactionIdentical to the standard Solana sendTransaction RPC. If you already talk to a Solana node, switching is a one-line change.
curl -X POST https://fast.circular.fi/transactions \
-H "x-api-key: YOUR_API_KEY" \
-H "Content-Type: application/json" \
-d '{
"jsonrpc": "2.0",
"id": 1,
"method": "sendTransaction",
"params": [
"<BASE64_TX>",
{
"cashbackAddress": "YourSolanaAddress"
}
]
}'
The same endpoint, any throughput.
All plans use the same URL and the same JSON-RPC format. Only your throughput ceiling changes.
Free
requests / second
Get started with no commitment. Great for testing and low-volume strategies.
Searcher
requests / second
For active traders who need consistent throughput without interruption.
Startup
Most popularrequests / second
High-frequency bots and production workloads that can't afford to be throttled.
Pro
Max performancerequests / second
Full access with priority routing and dedicated support for serious teams.
Need more credits or a higher limit?
Upgrade your plan on the Circular dashboard, no API change required.
View plans →Common questions
Fast is Circular's transaction broadcast service for Solana. When you submit a raw transaction, Fast simultaneously propagates it across staked validators, standard Solana nodes, and the Jito block engine to land it in the current slot, then monetizes it: the arbitrage your transaction leaks is captured and 65% of it is paid back to your cashback address in SOL.
Solana slots are 200ms long. A standard RPC usually gets your transaction in too late, so it is queued for the next slot, 200ms behind. Fast propagates wide enough and fast enough to land in the slot that is already open, which is what 0-slot means: zero slots of delay between sending and landing.
Your trade moves the price of a pool, which leaves an arbitrage on the table. On any other RPC a searcher backruns you and keeps all of it. Fast captures that arbitrage on your own transaction and sends 65% of the captured value in SOL to the cashbackAddress you include in your request. The remaining 35% covers execution and validator costs. There is nothing to claim and no extra API call.
It is optional but recommended: no cashbackAddress means no cashback to route. Pass any Solana address you control, including one different from the signer, and the SOL is credited there.
API keys are managed through the Circular dashboard. Visit docs.circular.fi/api/keys to create and manage your keys. Each key is tied to a subscription tier that determines your rate limits.
Fast supports multiple tiers: Free (25 RPS), Searcher (50 RPS), Startup (100 RPS), and Pro (100 RPS). All tiers use the same endpoint and the same JSON-RPC format. Only the throughput ceiling changes.
Yes. Fast and Jito bundles serve different purposes. Fast optimizes individual transaction propagation. Jito bundles allow you to submit ordered groups of transactions atomically. You can use Fast to broadcast your non-bundle transactions while still submitting bundles directly through the Jito block engine.
Yes. Fast uses the standard JSON-RPC 2.0 sendTransaction method. The only changes are the endpoint URL (fast.circular.fi/transactions) and the addition of the x-api-key header. The params array accepts Base58 or Base64 encoded transactions, just like any Solana RPC.