Which tools do Claude Code, Codex and Cursor choose?

The Armature team measured 16,893 sessions across 75 repositories and 10 languages to see which third-party services coding agents actually reach for. The headline is disagreement: the three agents picked the same tool only 42% of the time.

The behavioural differences are sharp. Claude Code leans on prior knowledge and searches the web about 30% of the time; Codex searches 94% of the time and Cursor 67%. Claude Code also builds in-house rather than adopting a dependency roughly twice as often, 19% against 10%. Repository context moves the answer, so the same request produces different email providers depending on whether the codebase is TypeScript, Python, Go or Java.

The finding with the most commercial sting is that being mentioned is not being chosen: PayPal came up 139 times and was never selected, LangChain 194 times and picked 4 times. Where concentration exists it is heavy, with Stripe at 90% of payments and Neon at 66% of databases, while email splits between Resend at 35.6% and Postmark at 27.4%. Method caveat worth carrying: the multi-turn conversations were simulated by a model and validated by another, so this measures agent behaviour under synthetic prompting rather than what developers actually shipped.