Debugging

Enable debug logs

Set RUST_LOG before starting the proxy:

RUST_LOG=litellm_rust=debug ./target/debug/lite --config config.yaml

For trace-level output (very verbose):

RUST_LOG=litellm_rust=trace ./target/debug/lite --config config.yaml

Router resolution

Every request logs how the incoming model name was resolved to an upstream deployment. Exact match — model name matched a named route in model_list:

router: exact match  model="claude" upstream_model="claude-sonnet-4-5" provider="anthropic"

Wildcard match — no exact match; fell through to the /* wildcard route. Provider prefix stripped if present:

router: wildcard match — stripped provider prefix  model="anthropic/claude-opus-4-8" upstream_model="claude-opus-4-8" provider="anthropic"

No route — no exact match and no wildcard configured:

router: no exact match and no wildcard route  model="gpt-4o"

Resolution is a single O(1) HashMap lookup — there is no retrying or brute-forcing.

Model cost map

On startup the proxy fetches the LiteLLM model pricing sheet. If the fetch fails it falls back to an embedded backup:

WARN Failed to fetch model cost map from https://... — using backup

If both fail (parse error, network issue), the proxy continues with an empty cost map and logs:

ERROR Failed to parse embedded backup model cost map: ...

Pricing data is used for cost tracking only — the proxy still routes requests normally with an empty map.

Config validation errors

Bad config exits immediately with a descriptive message:

Error	Cause
`model must include provider prefix`	`litellm_params.model` missing `provider/` prefix
`model missing name after provider prefix`	`litellm_params.model` set to just `anthropic/`
`unsupported provider: <id>`	Provider not registered (e.g. typo)
`missing litellm_params.api_key`	No API key for that model entry
`only one wildcard model route is supported`	More than one `/*` entry in `model_list`

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Engineering

Debugging

Debugging

Enable debug logs

Router resolution

Model cost map

Config validation errors

​Debugging

​Enable debug logs

​Router resolution

​Model cost map

​Config validation errors

Debugging

Enable debug logs

Router resolution

Model cost map

Config validation errors