# Universal Attributes
This document covers attributes that can be used on any span kind in OpenInference.
## Overview
These attributes can be used on **any span kind** to provide additional context, tracking, and metadata.
## Input/Output
| Attribute | Type | Description |
| ------------------ | ------ | ---------------------------------------------------- |
| `input.value` | String | Input to the operation (prompt, query, document) |
| `input.mime_type` | String | MIME type (e.g., "text/plain", "application/json") |
| `output.value` | String | Output from the operation (response, vector, result) |
| `output.mime_type` | String | MIME type of output |
**Example:**
```json
{
"openinference.span.kind": "CHAIN",
"input.value": "{\"question\": \"What is the weather?\"}",
"input.mime_type": "application/json",
"output.value": "{\"answer\": \"I don't have access to weather data.\"}",
"output.mime_type": "application/json"
}
```
## Session and User Tracking
| Attribute | Type | Description |
| ------------ | ------ | ---------------------------------------------- |
| `session.id` | String | Session identifier for grouping related traces |
| `user.id` | String | User identifier for per-user analysis |
**Example:**
```json
{
"openinference.span.kind": "LLM",
"session.id": "session_abc123",
"user.id": "user_xyz789"
}
```
## Metadata
| Attribute | Type | Description |
| ---------- | ------ | ------------------------------------------ |
| `metadata` | string | JSON-serialized object of key-value pairs |
**Example:**
```json
{
"openinference.span.kind": "LLM",
"metadata": "{\"environment\": \"production\", \"model_version\": \"v2.1\", \"cost_center\": \"engineering\"}"
}
```
