Edge TTS (Microsoft, community reverse-engineered)

Completely free with no official usage cap, accessed via the community-maintained open-source edge-tts tool

Not an officially documented API — it works by reverse-engineering Edge's Read Aloud service. High-frequency calls get rate-limited or blocked. Cloud IPs (e.g. Colab/Hugging Face Spaces) have recently become unstable due to anti-abuse token mechanisms.

⚠️Microsoft could tighten or shut down this interface at any time — the verification mechanism has already been adjusted multiple times historically. Not recommended as a production-level dependency.