Honest comparison
KeyForge vs Langfuse
Langfuse is the leading open-source LLM engineering platform, tracing, evals, prompt management, and analytics for teams building on LLMs. KeyForge is a security gateway for autonomous agents. They are often confused because both touch your LLM traffic, but they solve opposite problems: Langfuse helps you understand and improve what your app does; KeyForge controls and proves what your agents are allowed to do.
Where Langfuse is strong
Best-in-class tracing & evals
Nested trace trees, session grouping, dataset-based evals, LLM-as-judge scoring, and a prompt playground, the deepest developer observability toolkit in open source.
Open source & self-hostable
MIT-licensed core you can self-host for full data control, with a generous cloud free tier. Strong SDK coverage across Python, JS, and popular frameworks.
Prompt & experiment management
Versioned prompts, A/B experiments, and analytics that connect prompt changes to quality and cost metrics, built for iterating on LLM app quality.
Where KeyForge wins
Enforcement, not just observation
Langfuse observes traffic your app already decided to send, it does not sit in the request path to block or cap it. KeyForge is an inline gateway: it enforces per-key request quotas and dollar spend caps before the provider is ever called.
Virtual keys protect the credential
Langfuse traces requests but your agents still hold real provider keys. KeyForge issues vk_ virtual keys; the real credential is injected server-side and never seen by the agent, so a compromised agent leaks nothing.
Tamper-evident by cryptography
Langfuse stores traces in a database you (or it) can edit. KeyForge HMAC hash-chains every entry to the previous one, so insertion, deletion, or edits are mathematically detectable, evidence you can hand to an auditor or customer.
429 key-pool auto-shuffle
Langfuse records a rate-limit error after it happens; it cannot prevent it. KeyForge rotates to a fresh key from your pool on a 429 and replays the request on the same model, so the agent never sees the error.
Feature comparison
| Capability | Langfuse | KeyForge |
|---|---|---|
| Position in request path | Side-car observer (async) | Inline gateway (enforces before provider) |
| Credential handling | Agent holds real provider keys | vk_ virtual keys, real key never exposed |
| Spend control | Cost analytics after the fact | Hard per-key dollar caps, enforced live |
| Audit integrity | Editable trace database | HMAC hash-chained, verify + export |
| 429 handling | Records the error | Key-pool auto-shuffle, same model |
| Core strength | Tracing, evals, prompt ops | Key security, budgets, provable audit |
Frequently asked
Give your agents keys that can’t leak
Start with 3 virtual keys and the full HMAC audit chain, free. Migrating from Langfuse is a base-URL change.