modelprint

modelprint is a browser-based tool for fingerprinting OpenAI-compatible API endpoints and investigating which model or serving infrastructure may sit behind an alias. It sends controlled probes and compares results side by side, including normalized tokenizer counts for English, CJK, code, and rare Unicode inputs; template offsets; validation messages and error codes; maximum-output refusals; finish-reason vocabulary; router metadata; generation records; response headers; provider path behavior; context-window classes; and logprob geometry.

The tool runs without installation, a build step, or a server: API calls go directly from the browser to the provider, with keys retained in the browser tab. It can pin models to provider hosts to reduce routing noise and labels signals reported or validated by a router. Its documentation cautions that matching fingerprints indicate shared infrastructure or a model family rather than proving model identity, and that probes may report missing signals when headers, logprobs, or other telemetry are unavailable. The project supports community-authored probes through a defined JavaScript contract and is released under the MIT license.