The language

Strategy becomes an artifact.

Kestrel is the open-source language that turns a trading strategy into a compilable document: small enough to stay in an agent’s context, deterministic enough to grade, and diffable enough to review line by line. It ships MIT-licensed on npm, with the source and the language ADRs in the tarball.

One command, no box and no install ceremony. The bare invocation prints usage and exits clean; the workstation and the language ship together on npm.

npx kestrel.markets

Strategy as an artifact

Every agent framework re-invents "if-this-then-that under latency" as glue code: non-deterministic, wall-clock-infected, unreviewable. Kestrel does for trading reflexes what SQL did for data access. It makes the strategy a document, small enough to stay in context, precise enough to compile, and diffable enough to review a change line by line before it ever touches a market.

Determinism is the enabling property

Because the same plan replays byte-for-byte, everything above it becomes possible: a record you can certify, a benchmark that can grade, a reward signal that can train. Determinism is not a feature bolted onto the language. It is the property the rest of the platform is built on, which is why the notation and the substrate are one thing.

Speed is a corollary, not a feature

The plan runs at machine pace because the deliberating brain has structurally left the hot path. The strategy is written down, so the agent does not think at the tick; it reacts from what it already decided. Speed follows from writing the strategy down. It was never a separate thing to buy.

The artifact, verifiable

You do not have to take this page’s word for any of it. The package is open source, MIT-licensed on npm: the full TypeScript source, the examples, and the language ADRs are in the published tarball. Run npm pack kestrel.markets and read it, or browse the files without an account.

npm i kestrel.markets
npm pack kestrel.markets   # then read the tarball