# Coolhand vs Langfuse

> Langfuse traces and scores your LLM calls. Coolhand diagnoses what's wrong and opens the fix as a pull request.
> Here's how the two fit together.

## What is Langfuse?

Langfuse is an open-source LLM engineering platform: tracing, prompt version management, LLM-as-judge and
code-based evaluators, human annotation queues, datasets, and a prompt playground, built around a self-hostable,
MIT-licensed core. It was acquired by ClickHouse in January 2026, gaining an enterprise sales motion while
committing to keep the open-source core and self-hosting first-class.

It's genuinely good at capturing a detailed, queryable record of every LLM call your app makes, and letting you
score and annotate that record. What it doesn't do is turn a flagged issue into a code change — that's still on
your team.

## What Coolhand actually does

Coolhand watches your production AI agents continuously. When something breaks — a hard error, a quality
regression, a spike in cost — it diagnoses the root cause against your actual code, drafts the fix, and opens it
as a pull request in your repo. Nothing merges without a human reviewing it first. Alongside that, an open-source
skill audits your codebase for places to capture feedback that's already happening — edits, approvals,
corrections — instead of asking you to build a new annotation queue. Cost and quality dashboards then show whether
all of this is actually working, in dollars and quality-trend terms, not just "traces logged."

Where Coolhand excels: it's the only thing in this loop that turns a diagnosed problem into a reviewable code
change on its own, continuously and without per-issue manual triggering. It doesn't need an annotation team, a
dedicated eval engineer, or someone babysitting a dashboard — the loop runs in the background and only asks for
your attention when there's a PR to review.

That's the gap Langfuse leaves open: it will trace and score every call your agent makes, but it never turns that
signal into a fix. Coolhand picks up exactly where Langfuse's dashboard stops.

## Feature comparison

| Capability | Langfuse | Coolhand |
|---|---|---|
| Primary purpose | Trace, score, and manage prompts for LLM calls | Diagnose production issues and ship the fix as a PR |
| Tracing depth | Deep — hierarchical traces, sessions, cost/token dashboards | Request-level logs built for diagnosis, not a dedicated trace explorer |
| Evaluation | LLM-as-judge, code evaluators, datasets, playground | Correctness and sentiment evaluators feeding the diagnosis loop |
| Human feedback | Manual annotation queues | Passive capture from your app's existing UI — no queue to build or staff |
| Opens a PR with a fix | No — stops at detection and scoring | Yes — opens a real PR in your repo; you review and merge |
| Ingestion | Python/JS SDKs plus a generic OpenTelemetry endpoint | Ruby/Python/Node SDKs and provider proxies; no OpenTelemetry endpoint yet |
| Self-hostable server | Yes — MIT-licensed core, Docker or Kubernetes | No — managed service only (SDKs, CLI, and widget are open source) |
| ROI reporting | Cost and usage dashboards; ROI framing is on you | Cost-per-outcome and quality-trend dashboards built in |
| Pricing entry point | Free up to 50k units/month, then $29/month Core | Free up to 10M tokens/week |

## When you need both

If your team already leans on Langfuse for self-hosted trace storage, prompt versioning, or an OpenTelemetry
pipeline, keep it — Coolhand isn't trying to replace that. You need Coolhand alongside it once the question shifts
from "what happened" to "what do we change, and who's going to change it." Langfuse's annotation queues and
Monitors alerts flag that something's wrong; they don't diagnose the root cause against your code or draft the fix.

## How to use them together

Keep Langfuse as your system of record for traces, prompt versions, and self-hosted retention. Point Coolhand's
SDKs at the same production traffic. When Coolhand flags a recurring failure or a feedback-driven quality issue,
use Langfuse's trace view to inspect the specific calls behind it, then let Coolhand propose the fix as a PR — you
still review and merge it. Langfuse answers "show me exactly what this agent did," Coolhand answers "here's why
it's wrong and here's the fix."

## Frequently asked questions

**Does Langfuse open pull requests or fix code?**
No. Langfuse traces and scores every LLM call and supports annotation queues and Monitors alerts, but it stops at
detection and scoring — it doesn't diagnose the root cause against your code or draft the fix. Coolhand does, and
opens it as a pull request.

**Is Coolhand a replacement for Langfuse?**
No. Langfuse — open-source, MIT-licensed, and now part of ClickHouse — is a strong system of record for traces,
prompt versions, and self-hosted retention. Coolhand runs alongside it and picks up where its dashboard stops.

**What's the difference between Coolhand and Langfuse?**
Langfuse answers "show me exactly what this agent did." Coolhand answers "here's why it's wrong and here's the
fix," as a pull request you review and merge.

**Can I use Coolhand and Langfuse together?**
Yes. Keep Langfuse for trace storage and prompt versioning, point Coolhand at the same traffic, and use Langfuse's
trace view to inspect the calls behind a fix Coolhand proposes.

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Source: [coolhandlabs.com/beyond-observability/langfuse](https://coolhandlabs.com/beyond-observability/langfuse)