LLM Engineering🔴Developer

BAML

Name: BAML
Brand: BAML
Availability: InStock

A type-safe DSL from BoundaryML for writing LLM prompts as schema-validated functions in any language.

Starting atFree

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In Plain English

A type-safe DSL from BoundaryML for writing LLM prompts as schema-validated functions in any language.

Overview

BAML (Basically A Made-up Language) is an open-source domain-specific language from BoundaryML for building reliable LLM applications. Instead of stringly-typed prompts smeared across Python or TypeScript files, you write BAML files that declare functions with typed inputs, structured output schemas, and the prompt body that produces them.

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Difficulty:intermediate

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Key Features

Feature information is available on the official website.

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Pricing Plans

Open Source

Free

Boundary Studio Cloud

Usage-based

Enterprise

Custom

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Best Use Cases

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Replacing brittle string-templated prompts with typed functions

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Building agentic systems with structured tool calls

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Running deterministic prompt regression tests in CI

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Multi-language projects that share one prompt definition

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Teams that want to eval prompts without rewriting their stack

Pros & Cons

✓ Pros

✓Eliminates a whole class of brittle string-template prompt bugs
✓Polyglot codegen is a real win for multi-language stacks
✓Tests run in CI like any other unit test — prompt regressions stop being silent
✓Apache 2.0 core means no vendor lock-in on the prompt layer
✓Schema-aware JSON recovery handles common LLM output sloppiness

✗ Cons

✗It's a new DSL — onboarding cost for new contributors
✗Smaller community than LangChain, LlamaIndex, or raw SDK approaches
✗Studio pricing is opaque (on-application only)
✗Tooling outside VSCode is thinner than the in-editor experience
✗Overkill for one-off prototypes or simple single-prompt apps

Frequently Asked Questions

How much does BAML cost?+

BAML pricing starts at Free. They offer 3 pricing tiers including a free option.

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