langsmith-evaluator

langsmith-evaluator is a skill for Claude Code, Codex from joonlab/joonlab-claudecode-setting-for-share. It costs 83 tokens per session (3,644 once invoked), scanned C, a copy of langsmith-evaluator, MIT.

A skill for evaluating AI agents in LangSmith, a service for recording and assessing their runs. It covers evaluators, which judge results with a language model or custom code, plus local and automatic evaluation runs.

In plain words
What is it for?
Use it to capture agent outputs and execution paths, create quality checks, and run evaluation sets through LangSmith.
Why use it?
It gives you a way to measure whether an agent produces the expected results instead of relying only on manual checking. It also requires inspecting real sample outputs before writing evaluation logic.

Skill for Claude CodeCodex

Written for no agent in particular: nothing here depends on one. Also seen: mentions subagents.

Good fit Use it to capture agent outputs and execution paths, create quality checks, and run evaluation sets through LangSmith.

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Install with agentmods
npx agentmods add skills/joonlab/joonlab-claudecode-setting-for-share/langsmith-evaluator
Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

Any agent
npx skills add joonlab/joonlab-claudecode-setting-for-share --skill langsmith-evaluator
Clone the repo
git clone --depth 1 https://github.com/joonlab/joonlab-claudecode-setting-for-share

Made for: Claude Code, Codex.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

agentmods badge for langsmith-evaluator

README.md
[![agentmods](https://agentmods.dev/badge/skills/joonlab/joonlab-claudecode-setting-for-share/langsmith-evaluator/github.svg)](https://agentmods.dev/skills/joonlab/joonlab-claudecode-setting-for-share/langsmith-evaluator)
Your own site
<a href="https://agentmods.dev/skills/joonlab/joonlab-claudecode-setting-for-share/langsmith-evaluator"><img src="https://agentmods.dev/badge/skills/joonlab/joonlab-claudecode-setting-for-share/langsmith-evaluator/github.svg" alt="Measured on agentmods" height="20"></a>

Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.

agentmods 80×15 button for langsmith-evaluator

Your own site · 80×15
<a href="https://agentmods.dev/skills/joonlab/joonlab-claudecode-setting-for-share/langsmith-evaluator"><img src="https://agentmods.dev/badge/skills/joonlab/joonlab-claudecode-setting-for-share/langsmith-evaluator.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session 83 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 3,644 The whole file, excluding the scripts and references it only reads on demand.
Security scan C 2 findings. A grade says what 26 rules found in the file — not that it is safe.
Origin 89% copy Near-identical to another mod in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5.1 $0.00083 $0.03644
Opus 5 $0.00042 $0.01822
Sonnet 5 $0.00017 $0.00729
Haiku 4.5 $0.00008 $0.00364

Measured 9d ago against content hash b28078e85c10, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-09, from the pricing page.

Security

Grade C, and why

langsmith-evaluator scanned grade C with 2 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 9d ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Downloads and executes remote codehighSupply chain

curl | sh runs whatever the server returns today, which is not necessarily what it returned when this was reviewed.

curl -sSL https://raw.githubusercontent.com/langchain-ai/langsmith-cli/main/scripts/install.sh | sh

Makes network callslowCapability

Not a fault in itself. Listed so you know the mod talks to something, and to what.

curl -sSL https://raw.githubusercontent.com/langchain-ai/langsmith-cli/main/scripts/install.sh | sh
Origin

This is a copy

89% identical to langsmith-evaluator — 76 lines differ, which has more behind it and is treated as the original. This page carries a canonical link to it rather than competing with it.

claude/skills/langsmith-evaluator/SKILL.md · 363 lines

How it starts

The opening of the file, as written. The whole thing — 363 lines — stays where its author put it; the contents beside it link to each section on GitHub.

LANGSMITH_API_KEY=lsv2_pt_your_api_key_here          # Required
LANGSMITH_PROJECT=your-project-name                   # Check this to know which project has traces
LANGSMITH_WORKSPACE_ID=your-workspace-id              # Optional: for org-scoped keys
OPENAI_API_KEY=your_openai_key                        # For LLM as Judge

IMPORTANT: Always check the environment variables or .env file for LANGSMITH_PROJECT before querying or interacting with LangSmith. This tells you which project contains the relevant traces and data. If the LangSmith project is not available, use your best judgement to identify the right one.

Python Dependencies

pip install langsmith langchain-openai python-dotenv

CLI Tool (for uploading evaluators)

curl -sSL https://raw.githubusercontent.com/langchain-ai/langsmith-cli/main/scripts/install.sh | sh

JavaScript Dependencies

npm install langsmith openai

<crucial_requirement>

Golden Rule: Inspect Before You Implement

CRITICAL: Before writing ANY evaluator or extraction logic, you MUST:

  1. Run your agent on sample inputs and capture the actual output
  2. Inspect the output - print it, query LangSmith traces, understand the exact structure
  3. Only then write code that processes that output

Output structures vary significantly by framework, agent type, and configuration. Never assume the shape - always verify first. Query LangSmith traces to when outputs don't contain needed data to understand how to extract from execution. </crucial_requirement>

<evaluator_format>

Offline vs Online Evaluators

Offline Evaluators (attached to datasets):

  • Function signature: (run, example) - receives both run outputs and dataset example
  • Use case: Comparing agent outputs to expected values in a dataset
  • Upload with: --dataset "Dataset Name"

Read the full file on GitHub · 363 lines

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 9d ago First seen · 363 lines · 83 tokens per session scan C b28078e85c10

Subscribe to this mod's changes

langsmith-evaluator is a skill published in the GitHub repository joonlab/joonlab-claudecode-setting-for-share (10 stars, last pushed 1mo ago), licensed MIT. It adds 83 tokens to every session and 3,644 once invoked, about $0.0004 per session on Opus 5. A static security scan graded it C with 2 findings (downloads and executes remote code, makes network calls). It is 89% identical to langsmith-evaluator, differing in 76 lines, and is treated as a copy.

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