Kind 31990: Handler Information

Overview

A Handler Information event provides details about how an application can handle specific event kinds. This event contains URLs and protocols for redirecting users to specialized applications that can properly display and interact with specific types of content.

Specification

Property	Value
Kind Number	31990
Event Range	Replaceable (by d tag)
Defined in	NIP-89

Content Format

The content field can contain optional metadata in a JSON format similar to Kind 0 (User Metadata). This is especially useful when the pubkey creating the event is not the application itself.

Schema

{
  "name": "Application Name",
  "picture": "https://example.com/app-icon.png",
  "about": "Description of the application",
  "web": "https://app.example.com",
  "nip05": "[email protected]",
  "lud16": "[email protected]"
}

If the content is empty, clients should use the application's Kind 0 event for displaying information.

Tags

Tag Name	Description	Format	Required
d	Unique identifier	["d", "<random-id>"]	Yes
k	Supported event kind	["k", "<event-kind-number>"]	Yes
web	Web URL template	["web", "<url-with-bech32-placeholder>", "<optional-entity-type>"]	No
ios	iOS URL template	["ios", "<url-with-bech32-placeholder>", "<optional-entity-type>"]	No
android	Android URL template	["android", "<url-with-bech32-placeholder>", "<optional-entity-type>"]	No

• The d tag contains a random identifier for this handler event.
• The k tag specifies which event kind this application can handle. Multiple k tags can be included if the application handles multiple kinds.
• Platform tags (web, ios, android, etc.) provide URL templates where <bech32> in the URL should be replaced with the NIP-19 encoded entity to be loaded.
• The optional entity type (e.g., "nevent", "nprofile") specifies which NIP-19 entity type the URL handles.

Client Behavior

Clients should:

1. Fetch these events when a user wants to open an unknown event kind in a specialized application
2. Parse the URL templates and replace the <bech32> placeholder with the appropriate NIP-19 encoded entity
3. Direct the user to the appropriate application using the platform-specific URL
4. Display application information from either the content field or the application's Kind 0 event

Relay Behavior

Relays treat this kind like any other event. These events are replaceable by the d tag, so relays should replace old events with newer ones that have the same pubkey and d tag value.

Use Cases

• Defining how a code editor application can open code snippets (kind 1337)
• Specifying how a music player application can handle audio tracks
• Providing URLs for opening marketplace listings in specialized applications
• Enabling cross-application navigation for specialized content types

Example

{
  "kind": 31990,
  "pubkey": "1743058db7078661b94aaf4286429d97ee5257d14a86d6bfa54cb0482b876fb0",
  "content": "{\"name\":\"Code Viewer\",\"picture\":\"https://codeviewer.example.com/icon.png\",\"about\":\"A specialized application for viewing and editing code snippets\",\"web\":\"https://codeviewer.example.com\"}",
  "tags": [
    ["d", "abcd1234"],
    ["k", "1337"],
    ["web", "https://codeviewer.example.com/view/<bech32>", "nevent"],
    ["web", "https://codeviewer.example.com/user/<bech32>", "nprofile"],
    ["ios", "codeviewer://<bech32>"]
  ],
  "created_at": 1671217411
}

References

• NIP-89: Recommended Application Handlers
• NIP-19: bech32-encoded entities

Related Kinds

• Kind 31989: Handler Recommendation
• Kind 0: User Metadata
• Kind 1337: Code Snippet

Notes

Handler Information events create a bridge between general-purpose clients and specialized applications, enabling a more seamless user experience when interacting with specialized content types. The URL templates provide flexibility for different platforms while maintaining compatibility across the ecosystem.