litellm/litellm-rust/AGENTS.md

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AGENTS.md

litellm-rust has six crates. A crate is a layer, shared foundation, or separately built host, not a route. Routes (ocr, realtime, chat) and providers (mistral, openai) are modules inside the layers.

Crates

Crate Role
litellm-core The LiteLLM SDK in Rust. One public entrypoint per top-level call (messages::messages()), owning types, transforms, provider resolution, auth, and the provider HTTP call. Call it, get a typed response.
litellm-config Config-loading boundary. Returns resolved core deployment data and optionally delegates loading to Python.
litellm-gateway-inference Framework-independent gateway runtime and integrations shared by the server and Python bridge. Owns transport-neutral orchestration and legacy call modules, but no Axum or Tower dependencies.
litellm-gateway-server The root Axum binary and composition crate. Owns route composition, auth extractors, application state, startup config, and HTTP-only Tower dependencies, then delegates domain behavior to extracted gateway crates.
litellm-python-interop Domain-neutral PyO3 foundation for GIL handling and typed Python/Serde conversion.
litellm-python-bridge PyO3 cdylib exposing LiteLLM Rust APIs to the Python SDK. Owns API registration, domain wiring, and Python exception mapping.

Dependency direction is acyclic: litellm-config depends on litellm-core; litellm-gateway-inference depends on core; litellm-gateway-server depends on inference, core, and config; and litellm-python-bridge depends on the reusable domain layers and litellm-python-interop. Reusable crates must not depend on litellm-gateway-server. The interop foundation depends on no LiteLLM domain crate.

Where a route lives

A top-level LiteLLM call is a module under crates/core/src/<route>/, shaped like messages:

core/src/messages/
  mod.rs             # pub async fn messages(..) -> CoreResult<..>  (+ messages_stream for SSE)
  types.rs           # request/response types, MessagesRequest
  transformation.rs  # the provider template trait
  prepare.rs         # provider resolution, auth headers, URL
  handler.rs         # the provider call
  client.rs          # the shared reqwest client

Provider handlers never live in gateway-server. ocr, audio_transcription, and realtime provider I/O are still hosted in gateway-inference from before this rule; they move to core as they are touched.

Adding a crate: default to a module. A new crate requires a real trigger: separate artifact (binary/cdylib), proc-macro, shared foundation, or publishable standalone. A new provider or route is none of these.

Adding a crate fails crates/core/tests/workspace_crate_allowlist.rs until you update its allowlist and this file — intentional.

Style

All Rust in litellm-rust/ follows the official Rust Style Guide: https://doc.rust-lang.org/style-guide/

rustfmt implements its formatting by default, so run cargo fmt before committing; CI gates every PR on cargo fmt --check. Do not hand-format against rustfmt or add a rustfmt.toml that diverges from the default style.

Beyond formatting, follow the guide's naming and idiom conventions rustfmt cannot auto-apply: snake_case items/functions/modules, UpperCamelCase types/traits/variants, SCREAMING_SNAKE_CASE constants/statics (acronyms as one word, e.g. HttpClient), and the import grouping and item ordering it prescribes. See CLAUDE.md for the detailed version.