> ## Documentation Index
> Fetch the complete documentation index at: https://circle-devdocs-test-ai-codegen-component.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# Developer Services Glossary

Discover the essential building blocks that power Circle's Developer Services:

1. **Environments:** Understand the differences between Testnet (Sandbox) and
   Mainnet (Production) environments that facilitate the development and
   deployment.
2. **Wallets:** Explore the core functionality of wallets, facilitating secure
   storage and management of digital assets for your end-users.
3. **Wallet Sets:** Understand the concept behind wallet sets, which enable
   efficient management of multiple developer-controlled wallets.
4. **Users:** Streamline user interactions within Circle's Web3 ecosystem by
   simplifying pin and security question management for web3 wallets.
5. **Smart Contracts:** Explore smart contracts and our features that enable
   deployment and interaction.
6. **Transactions:** Delve into the transactional capabilities offered by
   Circle's Developer Services, empowering asset transfers, contract
   interactions, and deployments.
7. **Gas Station Policies:** Understand Gas Station policies and how they
   provide control for the sponsoring of gas fees.
8. **Monitored Tokens:** Enhanced control over token visibility, allowing
   selective filtering of tokens to enhance user experience.

By understanding these foundational components, you can unlock the full
potential of Circle's Developer Services and enhance your decentralized web
experiences.

<Accordion title="Video Tutorial: Understanding Circle Wallets Primitives">
  Watch this video to gain a fundamental understanding of Circle’s Developer
  Services building blocks. This video will help you grasp the basics of wallet
  functionality, the role of private keys, and how Circle’s API extends wallet
  capabilities with user-friendly flows and smart contract integration.

  <iframe src="https://fast.wistia.net/embed/iframe/uvtmej3rq7?seo=true&videoFoam=true" title="Video Tutorial: Understanding Circle Wallets Primitives" width="800px" height="450px" />
</Accordion>

## Environments

Circle supports two environments: Testnet (Sandbox) and Mainnet (Production).
When you initially sign up, you will be provided access to Testnet, which is
free to use. Once ready to promote to Mainnet, select “Access Mainnet” from the
developer dashboard and start the onboarding process.

* **Testnet:** Circle's Testnet environment acts as a Sandbox, enabling
  developers to safely test the functionality of Developer Services without the
  risks associated with a Production environment. Connected to blockchain
  Testnets, it provides a secure space to build applications and conduct testing
  before deployment.
* **Mainnet:** The Mainnet environment represents the Production environment
  where real user transactions and interactions occur. It is connected to the
  live blockchain network, ensuring the handling of real-world tokens.
  Developers should consider potential differences in blockchain confirmation
  times and gas fees when migrating from the Testnet to the Mainnet environment.

## Wallets

A Web3 Wallet, a decentralized or blockchain wallet, is a digital wallet that
allows users to securely store, manage, and interact with their crypto assets
and digital identities on the Web3 ecosystem. Unlike traditional wallets, Web3
wallets integrate with decentralized applications (dApps), enabling users to
authenticate, sign transactions, and interact with blockchain-based services.
With features like encryption and decentralized key management, Web3 wallets
provide users with control, privacy, and security over their digital assets and
interactions within the decentralized web.

Wallet attributes:

* **Address:**  An onchain identifier specific to a blockchain. It's worth
  noting that multiple wallets can share the same address on different EVM
  blockchains.
* **Custody Type:** Determines the control over the invocation of the wallet's
  private key, distinguishing between user-controlled and developer-controlled
  wallets. Explore the
  [Wallets infrastructure models](/wallets/infrastructure-models) for further
  insights.
* **Account Type:** Specifies whether the wallet is of the externally owned
  account (EOA) type or smart contract account (SCA) type.
* **Version Type:** Specifies the smart contract version for the SCA account
  type. By default, the modular smart contract account version is selected when
  this field is left blank.
* **State:** Indicates the current state of the wallet, signifying whether it is
  active or frozen.
* **Blockchain:** Identifies the blockchain and network to which the wallet
  belongs, providing context and compatibility information.

## Wallet sets

A wallet set is a
[hierarchical deterministic (HD) wallet](https://www.investopedia.com/terms/h/hd-wallet-hierarchical-deterministic-wallet.asp),
where all the children's wallets are created and managed by the same unique
cryptographic private key. For each developer-controlled wallet created, you
must provide a wallet set from which the wallet will be created.

Wallet set attributes:

* **Wallets:** A wallet set can contain one or many wallets. A wallet set can
  have wallets with addresses on multiple blockchains. On EVM chains, a wallet
  set can have wallets on different chains sharing the same address.
  * *maximum*: A single wallet set can potentially contain up to 10 million
    wallets.
  * *limitation*: An entity can create up to 1000 wallet sets. It is recommended
    to create as many wallets in a wallet set as needed.

For more information on creating and backfilling wallets with the same address,
see
[Unified Wallet Addressing on EVM Chains](/wallets/unified-wallet-addressing-evm).

## Users

A User represents an end-user of your application, allowing you to map their
account to associated wallets, tokens, and transactions. The `userId`, provided
during account creation, is a unique identifier connecting the user to these
components.

User attributes:

* **PIN:** A Personal Identification Number (PIN) enhances security by
  authenticating users when signing wallet transactions. Users must set up a
  unique numerical code PIN to access their account and perform sensitive
  actions.
* **Security Questions:** Users must set up security questions for account
  recovery, providing additional protection.
* **User Token:** The user token is a 60-minute session token utilized for
  requests requiring a user challenge, such as entering a PIN code. After
  expiration, a new user token is generated via the same endpoint.
* **Challenge:** Challenges act as checkpoints, prompting users to enter their
  PIN code to authorize critical actions like transactions or executing smart
  contracts. During user creation, the initial challenge guides users in setting
  their PIN code and Recovery Method, enabling account recovery if necessary.
* **Status:** Denotes whether the user is enabled or disabled, indicating their
  account's current operational state.

## Smart contracts

Smart contracts are the cornerstone of your deployed and onchain imported
contracts in Circle Contracts. To interact with a smart contract onchain, it is
necessary to import it first. All smart contracts deployed via the Developer
Services APIs can be readily interacted with by default. Once imported or
deployed, developers can leverage the functionality provided by the smart
contract. Contracts offers seamless accessibility to smart contracts through the
developer console and APIs.

With Contracts, developers can perform a wide range of tasks, including
deploying NFT contracts, creating onchain loyalty programs, interacting with
popular DeFi projects like Uniswap with just a few clicks, seamlessly
integrating Circle contracts (such as CCTP) into their apps, and deploying
custom contracts written specifically for their application needs.

## ABI (Application Binary Interface)

A smart contract Application Binary Interface (ABI) is a standardized interface
description for interacting with a smart contract deployed on a blockchain. It
defines the smart contract's structure, data types, and functions, enabling
seamless communication between the contract and external entities, such as user
interfaces, other contracts, or offchain applications.

The smart contract ABI serves as a contract's public interface, outlining how to
interact with it. It typically includes the following components:

1. **Function Signatures**: The names of the functions within the smart
   contract, along with their input and output parameter types. These signatures
   define the available operations that can be performed on the contract.
2. **Event Definitions:** Events provide information about specific occurrences
   or state changes within the contract. The ABI includes event definitions,
   specifying their names and the data associated with each event.
3. **Data Structures:** If the contract uses complex data structures or custom
   types, the ABI includes their definitions. Examples can include structs,
   arrays, or mappings.

The ABI allows developers and external applications to interact with a smart
contract without understanding the contract's underlying implementation details
or source code. It provides a standardized and language-agnostic way to
communicate with smart contracts, facilitating interoperability and seamless
integration with various platforms, tools, and services.

Smart contract attributes:

* **ID:** Once a smart contract is imported or deployed, Circle will assign an
  ID. This ID will be used in subsequent requests to read and execute the
  contract.
* **ABI Function Signature:** Used to specify the desired function to be read or
  executed. By providing the function signature, developers can effectively read
  data from the contract or trigger actions defined by that function.
* **ABI Parameters:** The parameters provided to the ABI function signature.
  Parameters are provided to the ABI function signature in the same order as
  received.
* **ABI JSON:** The contract's ABI in a JSON stringified format.
* **Functions:** Read and execute functions supported by the contract. The names
  of the functions in the smart contract, along with their input and output
  parameter types. These signatures define the available operations that can be
  performed on the contract.
* **Events:** Events the contract can emit. Events provide information about
  specific occurrences or state changes in the contract. The ABI includes event
  definitions, specifying their names and the data associated with each event.
* **Transactions:** List of onchain transactions executed on the contract. It is
  only available in the developer dashboard.

## Transactions

A transaction encompasses all blockchain activities, such as token transfers
(inbound or outbound), smart contract deployment, and smart contract execution.

Transactions also include metadata that outlines their state. Once a transaction
is created, Circle monitors the transactions on its respective networks
containing a state field. You can find more information about transaction states
in \[this guide]\(doc:asynchronous-states-and-statuses).

Each transaction includes an Operation field specifying the transfer's purpose
or use case. The table below highlights the various operations and their
corresponding destination address:

| **Operation Type** | Operation Field Value | Description of Destination Address Field Value             |
| ------------------ | --------------------- | ---------------------------------------------------------- |
| Transfer           | TRANSFER              | Externally owned account (EOA) that receives the transfer. |
| Execute            | CONTRACT\_EXECUTION   | Contract address.                                          |
| Deploy             | CONTRACT\_DEPLOY      | Deployment of a transaction.                               |

## Gas Station policies

The Gas Station Policy is a set of rules and configurations that govern the gas
fee sponsorship functionality, defining parameters and limitations for
subsidizing gas fees on a blockchain network for your application end-users.

For Mainnet, to enable gas fee sponsorship a policy must be activated. For
Testnet, Circle automatically preconfigures a policy for you at the time of
account creation. For Mainnet, you are required to configure them. Please see
Policy Management for more details.

Policy Attributes:

* **Network:** Specifies the blockchain network where the policy applies,
  ensuring compatibility and accurate gas fee calculation.
* **Maximum Daily Spend:** Sets the maximum allocated budget in USD for gas fee
  sponsorship within a 24-hour period. This limit helps manage and control the
  expenditure on gas fees.
* **Maximum Transaction Spend:** Optionally defines a cap on the amount of gas
  fees sponsored per individual transaction in USD. This allows for precise
  control over the financial commitment made for each transaction.
* **Maximum Operations per Day:** Optionally limits the number of daily
  operations (e.g., transactions) that can be sponsored. This parameter helps
  maintain a predetermined frequency and volume of sponsored operations.
* **Blocklist:** Optionally limits wallets that are eligible for gas
  sponsorship. This means that transactions initiated from these wallets will
  not have their gas fees covered. The blocklist allows for the selective
  exclusion of certain wallet addresses from receiving gas sponsorship.

## Monitor tokens

The Monitored Tokens feature in Circle Wallets empowers developers with enhanced
control over viewing token balances and transactions. This feature enables
developers to easily manage and filter out tokens unrelated to their use case
from our API responses, thereby selectively screening which tokens end-users can
see, providing a more streamlined and personalized experience. Using the APIs,
developers can easily add tokens via their unique token IDs.

By default, the system does not have any Monitored Tokens. This means that all
tokens are monitored without specific filtering or restrictions. The system will
track and monitor all tokens by default, providing comprehensive visibility and
monitoring for all token activities.

The monitor token supports native coins, ERC-20, ERC-721, and ERC-1155.

Monitor tokens attributes:

* **Token ID:** Each token deposited into a Circle Wallet generates a specific
  token ID, which developers can obtain by inspecting the tokens in wallets.
* **Token:** Associated attributes for the token, including names, the contract
  standard, the blockchain, decimal point, symbol, and the token's address.