BonsaiSafe expressions for rules, filters, and templates.

A constrained expression language for pricing rules, search filters, workflow conditions, and user-authored logic. Replace fragile eval()-style glue with typed errors, cacheable compilation, and real sandbox controls.

Open Playground

Read the Guide

GitHub

Zero runtime dependencies

Ships nothing into your dependency tree. Runs in Node 22+, Bun, and the browser.

Typed API and rich errors

Structured, discriminated error types with security codes and type guards — not thrown strings.

Safe by construction

Property allowlists, depth limits, and timeout guards. Built for expressions that come from config or end users.

Cacheable compilation

Compile once, evaluate on hot paths. Pluggable transforms and functions extend the language without unsafe escape hatches.

// Transform pipelines

" hello world " |> trim |> upper

→ "HELLO WORLD"

// Null-safe navigation

user?.profile?.avatar ?? "default.png"

→ "default.png"

// Lambda predicates

users |> filter(.age >= 18) |> map(.name)

→ ["Alice"]

Use it where `eval()` would be reckless

Pricing & Eligibility

Business Rules

A pricing rule changes every quarter. With Bonsai it is a text field in your admin panel that evaluates at runtime.

order.total
  >= freeShippingThreshold
  && customer.tier == "gold"

Search & Admin UIs

Filter Builders

Store a saved view as a string and evaluate it per row, with no custom query parser to build or maintain.

orders |> filter(
  .status == "pending"
  && .total > 500
)

Notifications & Emails

Templates

Template expressions live alongside the copy, not buried in application code or a separate engine.

`Hi ${user.firstName},
  order ${order.id} ships
  ${shipDate |> formatDate}`