# PoS Validators
PoS (Proof of Stake) Validators are **solo validators** who secure Mosaic Chain by running validator nodes and producing blocks. They stake exclusively via their Validator NFT's nominal value and operate independently without accepting delegations.
***
### **What PoS Validators Do**
PoS Validators are active participants in Mosaic Chain's consensus mechanism.
**Core responsibilities:**
* ✅ Run full validator nodes
* ✅ Produce new blocks (if selected by the subset algorithm)
* ✅ Validate transactions and maintain network security
* ✅ Stake via their Validator NFT's nominal value
* ✅ Earn block rewards and transaction fees
**In Polkadot terms:**
* Mosaic validators are technically **collators** (they collect transactions and produce blocks for the Polkadot relay chain to finalize)
* However, within Mosaic Chain's internal consensus, they function as **validators**
***
### **How Staking Works for PoS Validators**
PoS Validators have a unique staking model:
**Staking:**
* ✅ Stake **only via their Validator NFT's nominal value**
* ❌ **Cannot stake MOS coins**
* ❌ **Cannot accept delegations from others**
**Why this limitation?**
* PoS Validators are designed for **solo operation**
* Simpler setup with no delegation management
* Full control over their own stake and rewards
***
### **Requirements to Become a PoS Validator**
To participate as a PoS Validator, you must:
1. **Own and bind a PoS Validator NFT** - Grants permission to validate and represents your stake
2. **Run a validator node** - Using Validator OS (plug-and-play system)
3. **Maintain uptime** - Keep your node online and synced 24/7
4. **Be selected by the subset algorithm** - \~200 validators are randomly selected each session (1 hour)
***
### **PoS Validator NFTs**
The **PoS Validator NFT** represents both your permission to validate and your stake.
**Key features:**
* **Nominal value** - The NFT's nominal value is your stake (subject to slashing)
* **Transferable** - Can be sold or transferred to another account
* **Binding required** - Must be bound to your account to participate
* **Unbinding conditions** - Can only unbind if validator is chilled, not active, and the staking contract has ended
**Your stake = Your NFT's nominal value**
Unlike DPoS Validators who can add MOS coins to their stake, PoS Validators stake exclusively through their NFT's nominal value.
***
### **Rewards**
PoS Validators earn rewards from two sources:
#### **1. Block Rewards**
* Newly minted MOS coins (calculated via expansion formula)
* Distributed at the end of each session to active validators
#### **2. Transaction Fees**
* **50% of transaction fees** go to the block producer
* **100% of tips** go to the block producer
* **40% of fees are burnt** (removed from circulation)
* **10% of fees go to the Treasury**
**Reward distribution:**
* Rewards are distributed at the end of each **session** (1 hour ≈ 600 blocks)
* Only **active validators** (selected for that session) earn rewards
* PoS Validators keep **100% of their rewards** (no commission sharing)
***
### **Slashing & Auto-Chilling**
PoS Validators can be slashed for poor behavior or downtime.
#### **Slashing**
**What gets slashed:**
* **Validator NFT's nominal value** (0.1% of nominal value per slashing event)
**Slashing triggers:**
* Extended downtime
* Double-signing blocks
* Other malicious behavior
#### **Auto-Chilling**
Validators are automatically removed from the active set if:
1. **Slashed in two consecutive sessions**
2. **Validator NFT's nominal value drops below 80% of its initial value**
**Recovery:**
* Validators can unchill manually
* Validators must **top up their NFT's nominal value** to resume validation if it has dropped below 80% of its initial value
* After topping up, they can rejoin the waiting set
***
**Learn more:**
* [DPoS Validators →](/documentation/mosaic-chain/architecture-and-technology/actors-validators-and-delegators/dpos-validators.md) - Compare with delegation-accepting validators
* [Delegators (Stakers) →](/documentation/mosaic-chain/architecture-and-technology/actors-validators-and-delegators/delegators-stakers.md) - Learn about passive staking
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