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plugins/phoenix/skills/phoenix-tracing/references/fundamentals-universal-attributes.md

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+# 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                                  |
+
+### Why Capture I/O?
+
+**Always capture input/output for evaluation-ready spans:**
+- Phoenix evaluators (faithfulness, relevance, Q&A correctness) require `input.value` and `output.value`
+- Phoenix UI displays I/O prominently in trace views for debugging
+- Enables exporting I/O for creating fine-tuning datasets
+- Provides complete context for analyzing agent behavior
+
+**Example attributes:**
+
+```json
+{
+  "openinference.span.kind": "CHAIN",
+  "input.value": "What is the weather?",
+  "input.mime_type": "text/plain",
+  "output.value": "I don't have access to weather data.",
+  "output.mime_type": "text/plain"
+}
+```
+
+**See language-specific implementation:**
+- TypeScript: `instrumentation-manual-typescript.md`
+- Python: `instrumentation-manual-python.md`
+
+## 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\"}"
+}
+```