langsmith-fetch-skill

Why use it

Key features

Pulls traces directly from LangSmith Studio via CLI
Auto-triggers on debugging-flavored prompts
Tracks failures + root causes
Latency + token usage analysis
Tool-call and memory operation review
Session export

Live Demo

What it looks like in practice

langsmith-fetch-skill.replay ▶ ready

0/0

Install

Author repository · Claude Skills documentation

Use Cases

Real-world ways to use langsmith-fetch-skill

Diagnose a slow agent without opening LangSmith UI

👤 LangChain/LangGraph devs ⏱ ~20 min intermediate

When to use: An agent that used to be snappy is now slow; you want root cause.

Flow

Ask Claude to diagnose

Why is my agent <name> slow? Pull the last 20 traces from LangSmith and find the hotspot.✓ Copied

→ Skill fetches traces; reports latency by step
Drill in

Focus on trace <id> — break down tool-call times.✓ Copied

→ Per-tool latency with the outlier called out

Outcome: A specific step to optimize, not a hunch.

Pitfalls

Optimizing the average when tail latency is the problem — Ask for p95/p99 specifically

Combine with: filesystem

Root-cause an agent failure from a trace id

👤 Anyone running LangGraph in production ⏱ ~15 min intermediate

When to use: A user reported an error; you have the trace id.

Flow

Fetch + analyze

Debug trace <id>. What was the immediate error, what's the root cause in the graph?✓ Copied

→ Error step + upstream decision that led to it

Outcome: A fix targeting the actual decision point, not the symptom.

Find which node burns the most tokens

👤 Teams optimizing LLM spend ⏱ ~30 min intermediate

When to use: Monthly review of agent spend.

Flow

Aggregate token usage

Across last 7 days' traces, rank graph nodes by total token usage.✓ Copied

→ Ranked table with % share
Propose tightening

For the top 3, propose prompt-compression or model downgrade options.✓ Copied

→ Targeted opt list

Outcome: Measurable spend reduction without chasing tiny savings.

Combinations

Pair with other MCPs for X10 leverage

langsmith-fetch-skill + filesystem

Save exports alongside the agent code for lineage

Export the debugging session to debugging/traces/<date>.json.✓ Copied

langsmith-fetch-skill + github

Attach trace summary to a bug report

Summarize trace <id> and post as comment on GitHub issue #42.✓ Copied

Tools

What this MCP exposes

Tool	Inputs	When to call	Cost
fetch_recent	project, limit	Broad diagnosis	LangSmith quota
fetch_trace	trace_id	Deep dive on one run	LangSmith quota
analyze_failures	traces	Post-fetch analysis	0
export_session	traces	Archive for later	0

Cost & Limits

What this costs to run

API quota: LangSmith: depends on plan; Studio has generous quotas
Tokens per call: Low — traces are structured
Monetary: Free skill; LangSmith free tier covers most devs
Tip: Use fetch_recent with a narrow window, not full history

Security

Permissions, secrets, blast radius

Minimum scopes: LangSmith: read on your project(s)

Credential storage: LANGCHAIN_API_KEY in env

Data egress: Only to LangSmith (where the traces already live)

Never grant: Write to LangSmith — skill only reads

Traces can include user inputs and outputs — treat them as user data under your privacy policy.

Troubleshooting

Common errors and fixes

langsmith-fetch: command not found

Install LangSmith CLI or ensure it's on PATH

Verify: which langsmith-fetch

Empty results

Check project name and time window; traces are project-scoped

Alternatives