> ## Documentation Index
> Fetch the complete documentation index at: https://voltaire.tevm.sh/llms.txt
> Use this file to discover all available pages before exploring further.

# Message Format

> EIP-4361 SIWE message format specification

<Card title="Try it Live" icon="play" href="https://playground.tevm.sh?example=primitives/siwe.ts">
  Run SIWE examples in the interactive playground
</Card>

# Message Format

EIP-4361 SIWE message format specification.

## Format Structure

```
{domain} wants you to sign in with your Ethereum account:
{address}

{statement}

URI: {uri}
Version: {version}
Chain ID: {chainId}
Nonce: {nonce}
Issued At: {issuedAt}
Expiration Time: {expirationTime}
Not Before: {notBefore}
Request ID: {requestId}
Resources:
- {resource1}
- {resource2}
```

## Field Specifications

### Required Fields

#### domain

* **Type:** String
* **Format:** RFC 4501 dns authority
* **Position:** First line header
* **Example:** `example.com`
* **Rules:** Non-empty, no protocol, ASCII characters

#### address

* **Type:** Ethereum address
* **Format:** 0x-prefixed hex (42 chars)
* **Position:** Second line
* **Example:** `0x742d35Cc6634C0532925a3b844Bc9e7595f251e3`
* **Rules:** Exactly 40 hex characters after 0x, case insensitive

#### uri

* **Type:** String
* **Format:** RFC 3986 URI
* **Field:** `URI: {uri}`
* **Example:** `URI: https://example.com/login`
* **Rules:** Valid absolute URI

#### version

* **Type:** String
* **Format:** Version number
* **Field:** `Version: {version}`
* **Example:** `Version: 1`
* **Rules:** Must be "1" per current spec

#### chainId

* **Type:** Number
* **Format:** Decimal integer
* **Field:** `Chain ID: {chainId}`
* **Example:** `Chain ID: 1`
* **Rules:** Positive integer (>= 1), EIP-155 chain identifier

#### nonce

* **Type:** String
* **Format:** Alphanumeric
* **Field:** `Nonce: {nonce}`
* **Example:** `Nonce: a7b9c2d4e6f`
* **Rules:** Minimum 8 characters, cryptographically random, unique per request

#### issuedAt

* **Type:** String
* **Format:** ISO 8601 datetime
* **Field:** `Issued At: {issuedAt}`
* **Example:** `Issued At: 2021-09-30T16:25:24.000Z`
* **Rules:** Valid ISO 8601 format, UTC timezone

### Optional Fields

#### statement

* **Type:** String
* **Format:** UTF-8 text
* **Position:** Between address and field section
* **Rules:** Human-readable assertion, can be multi-line

#### expirationTime

* **Type:** String
* **Format:** ISO 8601 datetime
* **Field:** `Expiration Time: {expirationTime}`
* **Rules:** Should be after issuedAt, message invalid after this time

#### notBefore

* **Type:** String
* **Format:** ISO 8601 datetime
* **Field:** `Not Before: {notBefore}`
* **Rules:** Message invalid before this time

#### requestId

* **Type:** String
* **Format:** Any string
* **Field:** `Request ID: {requestId}`
* **Rules:** System-specific identifier

#### resources

* **Type:** Array of strings
* **Format:** List of URIs
* **Field:** `Resources:` followed by list items
* **Rules:** Each item prefixed with `- `, valid URIs

## Complete Examples

### Minimal Message

```
example.com wants you to sign in with your Ethereum account:
0x742d35Cc6634C0532925a3b844Bc9e7595f251e3

URI: https://example.com
Version: 1
Chain ID: 1
Nonce: abc123def
Issued At: 2021-09-30T16:25:24.000Z
```

### Full Message with All Fields

```
example.com wants you to sign in with your Ethereum account:
0x742d35Cc6634C0532925a3b844Bc9e7595f251e3

Sign in to Example App to access your account

URI: https://example.com/login
Version: 1
Chain ID: 1
Nonce: a7b9c2d4e6f8g0h1
Issued At: 2021-09-30T16:25:24.000Z
Expiration Time: 2021-10-01T16:25:24.000Z
Not Before: 2021-09-30T16:00:00.000Z
Request ID: req-abc123-xyz789
Resources:
- https://example.com/api/admin
- https://example.com/api/users
- https://example.com/api/settings
```

## Parsing Rules

### Field Ordering

Fields must appear in this order (if present):

1. URI (required)
2. Version (required)
3. Chain ID (required)
4. Nonce (required)
5. Issued At (required)
6. Expiration Time (optional)
7. Not Before (optional)
8. Request ID (optional)
9. Resources (optional, always last)

## Validation Rules

### Domain Validation

* Non-empty string
* No protocol prefix
* Valid DNS characters

### Address Validation

* 0x prefix required
* Exactly 40 hex characters
* Case insensitive

### Timestamp Validation

* Valid ISO 8601 format
* Must parse to valid Date
* Expiration must be after issuedAt

## Security Considerations

### Domain Binding

* Domain must match request origin
* Prevents cross-site authentication attacks

### Nonce Requirements

* Cryptographically random
* Minimum 8 characters
* Single-use only
* Prevents replay attacks

### Timestamp Validation

* Always validate server-side
* Consider clock skew
* Reject expired messages

## See Also

* [Siwe.format](/primitives/siwe/parsing) - Format message to string
* [Siwe.parse](/primitives/siwe/parsing) - Parse string to message
* [Siwe.validate](/primitives/siwe/validation) - Validate message structure
* [Siwe.create](/primitives/siwe/constructors) - Create message
* [EIP-4361: Sign-In with Ethereum](https://eips.ethereum.org/EIPS/eip-4361)