LangWatch

What it is for

LangWatch is an agent observability + eval desk: every user thread, trace, and span lands in one project, and you can run simulations against the same graph. Use it when the job is watch the agent and score it, not when you only need a gateway.

It is open source (langwatch/langwatch). Hosted Developer is €0 (50k events / month). Growth is €29 per core-seat / month.

What makes it unique: the cover is LangWatch’s official Traces chrome — thread / trace / span, the same view as New Traces Experience.

Key features

• Traces — one thread (user conversation), each trace (AI task), and the spans underneath in the same project (cover; Observability; official Traces video).
• Agent simulations — a simulated user runs a multi-turn scenario; a judge scores the conversation against your criteria (Agent Testing).
• Experiments — run a dataset through a prompt or agent, score every row, and compare runs before you ship (Experiments).
• Online evaluation — a monitor scores matching production traces or threads as they arrive (Online evaluation).
• Prompt versions — create, playground-test, and pin a prompt version the app can call (Prompt management).
• Alerts & automations — on a matching trace, email / Slack / webhook, add to a dataset, or enqueue for annotation; alerts fire when a graph series crosses a threshold (Alerts and automations).

Who it's for

Best fit: agent teams who will pay a core seat and send events from production.

Poor fit: teams that only want a $0 request proxy (Helicone).

Pricing

Verified 2026-10-22 (Asia/Shanghai) from langwatch.ai/pricing. Currency is EUR. Re-check checkout.

LangWatch Cloud

• Developer — €0. 50k events / month. 14-day data access. 2 users. 3 scenarios, 3 simulations, 3 custom evals. GitHub / Discord support. No credit card.
• Growth — €29 / core-seat / month. 200k events included, then €5 / 100k. 30-day retention (extend €3 / GB). Unlimited lite-users, simulations, evals, prompts. Private Slack / Teams. Volume discounts above 20 users.
• Enterprise — custom. Hybrid / self-hosted / on-prem, SSO / RBAC, audit logs, SLAs, ISO 27001, marketplace billing.

Self-Managed is a separate toggle on the same page.

Limitations / costs

• €29 is per core-seat, not per lite-user.
• Events meter after 200k on Growth (€5 / 100k).
• Developer is 50k events and 14 days.
• Prices are EUR. Do not paste a USD $29 without converting.

Alternatives

• Braintrust — evals + traces with a $249 Pro platform fee.
• Langfuse — open-source traces if you will self-host first.
• Helicone — gateway + logs if you do not need simulations.

Official tutorial

Official LangWatch channel video: New Traces Experience - Agent observability (oEmbed author: LangWatch).

Written path: Quick start plus Pricing.

Website

https://langwatch.ai

Repository

https://github.com/langwatch/langwatch

Source

Catalog row curated for AI Tools Nav. Cover is LangWatch’s official Traces chrome. Developer €0 / 50k events; Growth €29/core-seat. Tutorial: Traces on @LangWatch (oEmbed).

Last verified

2026-10-22 (Asia/Shanghai) editorial check.