Which integrations are available for this server?

Generates telephony-ready text-to-speech audio in Asterisk-compatible formats such as raw signed linear (sln/sln16) and G.711 µ-law/A-law, suitable for PBX announcements.

How do I use RestfulTTS?

1. Click on "Deploy Server". 2. Wait a few minutes for the server to deploy. Once ready, it will show a "Started" state. 3. In the chat, type @ followed by the MCP server name and your instructions, e.g., "@RestfulTTS Convert 'Welcome to the office' to English speech as a WAV file." That's it! The server will respond to your query, and you can continue using it as needed. Here is a step-by-step guide with screenshots.

RestfulTTS

by PhonixPBX

Overview Schema Source Related Servers Discussions Admin

Python

Remote

RestfulTTS

Text-to-speech for PhonixPBX announcements, served over a REST API, an MCP server and a small web UI.

Language	Voices	Model
German (`de`)	`thorsten` (neutral)	Thorsten-Voice/Kokoro, a Kokoro-82M fine-tune on the CC0 Thorsten-Voice dataset
English (`en`)	`af_heart` (default), `af_bella`, `am_michael`, `bf_emma`, `bm_george`	hexgrad/Kokoro-82M
French (`fr`)	`ff_siwis`	hexgrad/Kokoro-82M
Italian (`it`)	`if_sara` (default), `im_nicola`	hexgrad/Kokoro-82M; both voices are only graded "C" by Kokoro

Inspired by nazdridoy/kokoro-tts. Unlike that project, it uses the PyTorch kokoro package instead of kokoro-onnx, because the German model only exists as a PyTorch checkpoint. It also needs the semidark forks of kokoro and misaki; only those forks contain the German G2P.

Run

With Podman (CPU only), from the released image (linux/amd64 and linux/arm64):

podman run -d -p 8000:8000 -v restfultts_data:/data ghcr.io/phonixpbx/restfultts:latest

Or built from source:

podman-compose up -d            # or: podman build -t restfultts . && podman run -p 8000:8000 -v restfultts_data:/data restfultts

The first start downloads about 650 MB of models and voices into the /data volume, which can take several minutes. Later starts load them from the volume.

Locally with uv and Python 3.12:

uv sync --extra dev
uv run restfultts download          # optional: fetch all models up front
uv run restfultts serve             # http://127.0.0.1:8000
uv run restfultts say "Guten Tag." -o hallo.wav
uv run restfultts say "Buongiorno." -l it -f ulaw -o hallo.ulaw

The UI is at /, the OpenAPI docs are at /docs, and the MCP endpoint is /mcp.

Related MCP server: TTS MCP Server

Configuration

Environment variables (or an .env file):

Variable	Default	Description
`RESTFULTTS_API_TOKEN`	empty	When set, REST and MCP need `Authorization: Bearer <token>` and the UI asks for the token. Empty means open access, so only use that on a trusted network.
`RESTFULTTS_DATA_DIR`	`data` (`/data` in the container)	Holds the audio cache. In the container it also holds the models (`HF_HOME=/data/hf`).
`RESTFULTTS_PRELOAD`	empty (`de,en,fr,it` in the container)	Languages whose models are loaded at startup; others load on the first request.
`RESTFULTTS_DEVICE`	`auto`	`cpu`, `cuda` or `auto`. The container ships CPU-only PyTorch.
`RESTFULTTS_THORSTEN_EPOCH`	`5`	Checkpoint of the German model (1–10).
`RESTFULTTS_MAX_TEXT_CHARS`	`5000`	Longer texts are rejected with 413.
`RESTFULTTS_CACHE_MAX_MB`	`1024`	Size limit of the audio cache; the least recently used files are removed first.
`RESTFULTTS_HOST` / `RESTFULTTS_PORT`	`127.0.0.1` / `8000`	Listen address (`0.0.0.0` in the container).
`RESTFULTTS_ALLOWED_HOSTS`	empty	Comma separated host names the server answers to, e.g. `tts.example.org,.pbx.lan`; `` allows any. Other `Host` headers get 400, which protects against DNS rebinding. When empty, only `localhost` and `127.0.0.1` are allowed while listening on loopback, and any host otherwise.

REST API

Method and path	Description
`POST /api/v1/synthesize`	Body `{"text", "voice"?, "language"?, "speed"? (0.5–2.0), "format"?}`. Returns the audio bytes. Give either `voice` or `language`; with only a language you get its default voice.
`GET /api/v1/synthesize?text=…&language=…&format=…`	Same as `POST`, for clients that can only fetch a URL.
`GET /api/v1/audio/<hash>.<ext>`	A file from the cache.
`DELETE /api/v1/audio/<hash>`	Deletes a file from the cache, with all formats derived from the same synthesis. Returns 204, or 404 if it is not in the cache.
`GET /api/v1/voices?language=de`, `/api/v1/languages`, `/api/v1/formats`, `/api/v1/health`	Metadata.
`POST /tts`	Compatible with the `thorstenvoice/kokoro-tts` container. `{"text": "..."}` returns German WAV.

Synthesis responses carry the headers X-Cache: hit|miss and X-Voice.

Formats:

Format	Rate	Content
`wav`	24 kHz	Original quality
`wav16`	16 kHz	WAV
`wav8`	8 kHz	WAV
`sln`	8 kHz	Asterisk raw signed linear, 16 bit
`sln16`	16 kHz	Asterisk raw signed linear, 16 bit
`ulaw`	8 kHz	Raw G.711 µ-law
`alaw`	8 kHz	Raw G.711 A-law

The G.711 encoders give the same output as Python's audioop for every 16-bit sample.

curl -o ansage.wav -H 'Content-Type: application/json' \
     -d '{"text": "Guten Tag und willkommen."}' http://localhost:8000/tts
curl -o ansage.ulaw 'http://localhost:8000/api/v1/synthesize?text=Benvenuti&language=it&format=ulaw'

Each text is synthesized once and cached as 24 kHz WAV. Other formats of the same text are derived from that file.

MCP

The MCP endpoint uses Streamable HTTP (stateless, JSON responses) at http://<host>:8000/mcp. If a token is configured, clients send it as a bearer token. It offers three tools:

list_voices(language?)
list_formats()
delete_audio(url) deletes a file and all its formats.
synthesize(text, voice?, language?, speed?, format?) returns the audio as MCP audio content, plus a JSON text with the voice, the duration and the download path.

claude mcp add --transport http restfultts http://localhost:8000/mcp --header "Authorization: Bearer $TOKEN"

Development

uv run pytest -q                    # unit, API, MCP and UI tests with a fake engine
uv run pytest -m models             # real synthesis in all four languages (downloads the models)
uv run ruff check . && uv run ruff format --check . && uv run mypy src
scripts/test-container.sh <image>   # smoke test of a built image, as in CI
scripts/vendor-update.sh            # refresh Tabler 1.7.1 / htmx 4.0.0 (same versions as PhonixPBX)

Releases are tagged vX.Y.Z. CI then builds and pushes the container image and creates the GitHub release from CHANGELOG.md; see docs/RELEASING.md.

Licenses

RestfulTTS is licensed under Apache-2.0. Both models are Apache-2.0, and the Thorsten-Voice dataset is CC0.

For phonemization, misaki uses espeak-ng through phonemizer-fork and espeakng-loader. Both are GPL-3 and are installed as unmodified Python dependencies. Unlike in PhonixPBX, espeak-ng does not produce the speech here; it only converts text to phonemes for Kokoro. See NOTICE.

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Maintenance

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RestfulTTS

Run

Configuration

REST API

MCP

Development

Licenses

Maintenance

Resources

Related MCP Connectors

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