litellm/litellm-rust/AGENTS.md

AGENTS.md

litellm-rust has exactly THREE crates. A crate is a LAYER, 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-ai-gateway	The axum server (behind the server feature) plus the WebSocket hosts. Translates HTTP/WS to core entrypoints; owns no provider logic and no handlers.
litellm-python-bridge	PyO3 cdylib exposing Rust to the litellm Python SDK — marshals Python objects and calls core entrypoints.

Dependency direction (acyclic): litellm-core ← litellm-ai-gateway ← litellm-python-bridge.

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

Handlers never live in ai-gateway. ocr, audio_transcription, and realtime are still hosted there from before this rule; they move to core as they are touched.

Adding a crate: default to a MODULE. New crate ONLY on 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.