Tools that trace, test, evaluate and guard LLM apps and AI agents in production.
153
companies on usedby use a tool of this category
153 companies on usedby use at least one of the 6 tools in this category with a public customer. LangSmith leads with 43 companies. Then come Braintrust (42) and Arize AI (35). 6 companies run two of these tools or more. The most common pair is LangSmith with Galileo (2 companies).Latest check Oct 14, 2026: 149 of 160 public lines checked. Counts are of companies on usedby, not of the whole market: we list a company when a public page shows its AI tools.
Companies with a public line for each tool. Job-post signals count and are drawn apart in the proof bar.
| # | Tool | Customers | Proof |
|---|---|---|---|
| 1 |  LangSmith | 43 | |
| 2 |  Braintrust | 42 | |
| 3 |  Arize AI | 35 | |
| 4 |  Comet Opik | 17 | |
| 5 |  Galileo | 13 | |
| 6 |  Fiddler AI | 10 |
6 companies run two of these tools or more. The most common pair is LangSmith with Galileo, at 2 companies.
LangSmithLangSmith is used by 43 companies on usedby, 0 confirmed by a case study, a named quote or a press release. Customers include Nvidia, Toyota, and Cisco. Who uses LangSmith, Arize AI vs LangSmith
Customer page: langchain.com. Latest check of 37 of 43 lines: Oct 13, 2026.
BraintrustBraintrust is used by 42 companies on usedby, 12 confirmed by a case study, a named quote or a press release. Customers include Cloudflare, Coursera, and Dropbox. Who uses Braintrust, Braintrust vs Browserbase
Customer page: braintrust.dev. Latest check of 42 of 42 lines: Oct 14, 2026.
Arize AIArize AI is used by 35 companies on usedby, 7 confirmed by a case study, a named quote or a press release. Customers include Booking.com, Tripadvisor, and PagerDuty. Who uses Arize AI, Arize AI vs LangSmith
Customer page: arize.com. Latest check of 30 of 35 lines: Oct 5, 2026.
Comet OpikComet Opik is used by 17 companies on usedby, 10 confirmed by a case study, a named quote or a press release. Customers include Uber, NTT Data, and Ancestry. Who uses Comet Opik, Comet Opik vs LangSmith
Customer page: comet.com. Latest check of 17 of 17 lines: Oct 7, 2026.
Companies first listed by a tool of this category in the last 90 days.
Side-by-side pages with the companies behind each tool.
Answers drawn from usedby data.
LangSmith, used by 43 of the 153 companies on usedby in this category. Then come Braintrust (42) and Arize AI (35). Who uses LangSmith.
LangSmith: 43 companies on usedby, against 42 for Braintrust.
Yes: 6 of the 153 companies on usedby in this category run two or more. The most common pair is LangSmith with Galileo (2 companies).
By the number of companies with a public line for each tool, read from dated captures of vendor customer pages, case studies, press releases and job posts. Every proof level counts in the totals and the ranking, job-post signals included (the weakest proof, shown apart in the proof bar); ties go to the stronger proofs. usedby lists a company when a public page shows it, so these counts describe the companies on usedby, not the whole market.
