Langfuse Observation View
Display detailed information for a specific Observation (Generation/Span).
Setup
Set the following environment variables before use:
| Variable | Required | Description |
|---|---|---|
LANGFUSE_PUBLIC_KEY | Yes | Langfuse public key |
LANGFUSE_SECRET_KEY | Yes | Langfuse secret key |
LANGFUSE_HOST or LANGFUSE_BASE_URL | No | Langfuse host URL (default: https://us.cloud.langfuse.com) |
When to Use
- Checking specific LLM call details
- Viewing input/output
- Checking costs and token usage
- Viewing prompts used
Commands
1. Get Observation Details
npx tsx scripts/langfuse-observation-view.ts <observationId>
2. Show Full Input/Output
npx tsx scripts/langfuse-observation-view.ts <observationId> --full
3. JSON Output
npx tsx scripts/langfuse-observation-view.ts <observationId> --json
Output Example
Langfuse Observation Detail
===========================
ID: obs_abc123
Trace ID: trace_xyz789
Type: GENERATION
Name: chat
Start Time: 2026-01-21 10:30:45
Duration: 2.35s
Level: DEFAULT
--- Model Info ---
Model: qwen/qwen3-32b
Parameters: {"temperature":0.7}
--- Usage & Cost ---
Input Tokens: 1500
Output Tokens: 350
Total Tokens: 1850
Input Cost: $0.000435
Output Cost: $0.000207
Total Cost: $0.000642
--- Prompt ---
Prompt: librarian-system (v3)
Prompt ID: prompt_def456
--- Input ---
[{"role":"system","content":"You are..."}]
--- Output ---
Here are the search results...
Fields
| Field | Description |
|---|---|
| Type | GENERATION (LLM call), SPAN (processing span), EVENT (event) |
| Duration | Processing time |
| Model | Model used |
| Input/Output Tokens | Token usage |
| Calculated Cost | Computed cost |
| Prompt | Langfuse prompt used |