For newbies, https://mempool.space/
For those that are no more newbies: https://jochen-hoenicke.de/queue/#BTC,24h,weight
For advanced users: Run full node to view the mempool. Not encouraging but actually worth it if you can, for privacy.
I am still surprised that there is option many years ago for replace-by-fee (RBF) to pump bitcoin unconfirmed transaction but many wallets are not supporting it, after many of the wallets are close source, some people that do not know much about bitcoin wallets are using them. This has resulted to many people to be complaining about unconfirmed transaction that will need an option that will be more difficult to solve, instead to use RBF, but the wallet used not support RBF. Newbies need to know what RBF is because it is the easiest means to accelerate bitcoin transaction.
Disadvantages of other means of accelerating bitcoin transactions
Free and paid accelerators
There are different ways you can accelerate bitcoin transaction, example is the free accelerator provided by mining pool like ViaBTC, another are the paid accelerator also provided by some mining pools. The disadvantages is that if the mempool is very congested, making use of free accelerator like that one provided by ViaBTC becomes difficult because more people making use of the service at the time of congestion, making your transaction not to be included among the ones to be accelerated, while paid accelerator will demand for a very high fee which makes it not possible for many people to use it, mining pool can demand for $700 or more to just accelerate a bitcoin transaction of $10, $21, $1000 or more. Paid accelerator is not an advisable option to use.
Another disadvantage of accelerator is that it is offered individually by mining pool, even if the mining pool has included a transaction to be accelerated, it would only be included in the block mined by the mining pool. If the mining pool is not contributing much hashrate, the chances it is would mine a block is low, which is the block the transaction will be included. But the mining pool will actually mine a block sooner or later.
CPFP
Another means to accelerate bitcoin transaction is the use of child-pay-for-parent. One of the disadvantages is that it may not be simple for newbies to understand. Another is that it requires more transaction fee, which means you will pay more transaction fee in accordance to the present mempool fee rate priority (sat/vbyte), the transaction weight or virtual size of the old and new transaction and the fee paid for the old transaction. But this is the best option left for those that are using wallets that do not support RBF. You can read more about it through these links:
Guides for CPFP
[Guide] Use CPFP if your stucked transactions from blockchain.com wallet
How Replace-By-Fee (RBF) and Child-Pays-For-Parent (CPFP) can speed up confirmation
[TUTORIAL]getting a low-fee transaction unstuck by creating a CPFP with electrum
RBF vs CPFP
A good SPV wallet to use for CPFP is Electrum, or any other wallet that has coin control.
What is RBF and how it works
Very simple, assuming you have made a bitcoin transaction, using a low fee, or the mempool become more congested and your transaction remain unconfirmed, you can easily pump the fee if the wallet you used for the transaction supports RBF, but not all wallets that supports it, resulting to inability to pump the fee to make the transaction get confirmed as early as possible. This is the reason for this topic, to let newbies know how important RBF is and to know the wallets that supports RBF.
Open source wallets that supports RBF
Bitcoin Core
Fully Noded
Electrum
Bluewallet
Trezor Suite
Blockstream Green
Samourai
Sparrow wallet
Specter wallet
Nunchuk (Disadvantage: Supporting email account registration and encrypted cloud backup). Best to backup seed phrase offline.
Wasabi
Coinb.in (not recommend for beginners). Read this and this.
Note: No close source wallet mentioned, if there is any, let me know so I can edit and correct it. No custodial wallet mentioned, because of obvious reason of not your key not your coin.
If you are using one of those non-recommendable wallets before reading this topic, and the transaction fee used is or more than 10 sat/byte (not vbyte) and the transaction size not more than 500 bytes, you can use VIABTC free accelerator. But note that if ViaBTC include your transaction, it will only be confirmed after ViaBTC mined a block if it has not been confirmed naturally by mempool decongestion.
Free BTC transaction accelerator!
Lastly, have you heard about full RBF? Nothing like that has been implemented, but maybe it would be possible in the future, you can follow this thread about it:
Full RBF
It has been implement. The mempoolfullrbf option is part of Bitcoin Core v24.0, which will be released in the coming days. I don't think it will take too long before the network starts to adopt it, especially given that miners will make more profit if they do and will lose out on profits to other miners if they don't. It won't be long before opting in to RBF is a thing of the past. Every transaction will be eligible to be RBFed - the only stipulation is whether or not your wallet software will let you do it (but you can always import your seed phrase/private keys to a better piece of software if needed).
You can read more on full RBF from the release note of the latest Bitcoin Core that was released few weeeks ago: https://github.com/bitcoin/bitcoin/blob/master/doc/release-notes/release-notes-24.0.md