Observability tells you what happened. FAULTLINE tells you whether to ship.
Keep your tracing tool. FAULTLINE reads the same OpenTelemetry traces and turns them into a release verdict in CI.
01 / TWO DIFFERENT JOBS
Observability and eval platforms
Record traces
Dashboards and scores
A person decides
FAULTLINE
Record traces
Noise band + rule checks
PASS / FAIL / INCONCLUSIVE in CI, failing step named
02 / PLATFORM COMPARISON
| Dimension | FAULTLINE | Braintrust | LangSmith | Confident AI | Arthur | Galileo | Patronus AI |
|---|---|---|---|---|---|---|---|
| Main job | Release verdict on agent changes | Tracing and evals | Tracing, evals, agent deployment | LLM evals (DeepEval) | Monitoring, governance, LLM firewall | Evals, observability, guardrails | Evaluator models, benchmarks |
| How the CI gate decides | Significance test vs your measured noise. Business rules are a hard block. Says how many more runs it needs. | Thresholds via custom reporters; no formal statistical test | Not compared | Not compared | Not compared | Not compared | Not compared |
| Published entry price | $0 open source. Gate $1,500 / agent / mo | $0 Starter. Pro $249 / mo | $0 Developer. Plus $39 / seat / mo | $0 Free. Starter $200 / mo | $0 Free. Premium $60 / mo | Now sold through Splunk (Cisco) | Not published |
| What grows your bill | Number of agents. Nothing is metered. | Processed data ($3–4 / GB) and scores ($1.50–2.50 / 1k) over allowance | Traces over allowance, and seats | Trace storage, $1 / GB-month over allowance | Usage quotas on jobs, spans, inferences, evals | Splunk pricing | Contact sales |
| Where your traces go | Stay in your CI. Nothing uploaded. | Their cloud, or on-prem on Enterprise | Their cloud, or self-hosted on Enterprise | Their cloud, or self-hosted on Enterprise | Their cloud, or VPC on Enterprise | Their cloud, or VPC on Enterprise | Their cloud, or private deployment on Enterprise |
| Default grader | Deterministic code checks. Model judge optional. | Scorers you configure | Evaluators you configure | 50+ metrics, many model-graded | Rules and evaluators you configure | Luna evaluator models | Evaluator models (Lynx, GLIDER) |
| faultgate reads its exports | – | Yes | Yes | Not compared | Not compared | Not compared | Not compared |
| Best at | Ship / no-ship decision, noise-aware | Hosted tracing, prompt playground, evals at scale | LangChain and LangGraph ecosystem | Breadth of metrics, red teaming | Enterprise governance, agent discovery | Evaluator models, runtime guardrails | Research benchmarks, evaluator models |
Prices from each vendor's public pricing page, checked 12 October 2026. Prices change; check the vendor's site.
03 / OPEN SOURCE
The open-source tools, side by side.
| Dimension | faultgate | Promptfoo | DeepEval | Langfuse | Inspect AI | Arize Phoenix |
|---|---|---|---|---|---|---|
| Licence | MIT | MIT | Apache-2.0 | MIT core, ee/ commercial | MIT | Elastic License 2.0 (not OSI open source) |
| Owned by | Faultline (independent) | OpenAI (acquisition announced Mar 2026) | Confident AI | ClickHouse (acquired Jan 2026) | UK AI Security Institute | Arize AI |
| Main job | Release gate on recorded agent traces | Prompt and agent evals, red teaming | LLM eval metrics, 50+ | Tracing, prompts, evals | Eval framework: tasks, solvers, scorers | Tracing and evals |
| How the CI gate decides | Significance test vs measured noise; INCONCLUSIVE with required sample size | Repeat k-of-n (repeat-min-pass) and fail-on-threshold | Not compared | Threshold or regression vs approved baseline, single pass, no multi-run statistics | Not compared | Not compared |
| Business rules on tool arguments (limits, identity, order) as a hard block | Yes | Not compared | Not compared | Not compared | Not compared | Not compared |
| faultgate reads its exports | – | Not compared | Not compared | Yes | Not compared | Yes (OpenInference) |
These are good tools and many teams should keep using them. faultgate reads their exports. What it adds is the release decision: business rules as a hard block, and a significance test instead of a threshold.
Checked 7 October 2026.
THE HONEST PART
Several of these tools also run repeated trials and custom code checks. We are not replacing your tracing tool. faultgate reads standard OpenTelemetry GenAI traces, so it runs next to any of them. What none of them sells is the combination below.
04 / THE COMBINATION
A verdict, not a dashboard
PASS / FAIL / INCONCLUSIVE with the failing step named.
Regression or noise
Your noise band is measured before anything is judged.
Local-first
Traces never leave your CI.
Deterministic first
Code checks need no model; a judge only when you ask.
Flat per agent
Run CI 10 or 10,000 times, same bill.
Business rules as a hard block
A refund over the limit fails even inside the noise band.
GET STARTED
See it on your own traces
Install faultgate locally in seconds or speak with us about gating your production agent fleet.
pip install faultgate