Free tools API

The free tools on voicelabs.now also answer over HTTP, with no API key and no account. They are separate from the Developer API: that one is keyed and part of VoiceLabs Pro; these are small utilities anyone can call from a script, a CI job or an AI agent.

The OpenAPI 3.1 document for them is at https://voicelabs.now/api/tools/openapi.json. Every operation in it has security: [] and the tag Free tools.

The contract

• No authentication. Nothing is read from cookies or headers to identify you, so CORS is *.
• POST a JSON body, a form, or multipart/form-data with the file in the file field.
• GET takes the same fields as query parameters, for small inputs.
• JSON by default. Send Accept: text/markdown to get the result as a Markdown document instead, or download=1 to get the resulting file itself with a Content-Disposition: attachment header.
• Errors are RFC 9457 problem documents (application/problem+json) with title, status and a detail written for a person.
• Rate limit: 30 calls a minute and 300 a day per address. Past either, the answer is 429 with a Retry-After header.
• Every response carries X-Tool-Docs: https://voicelabs.now/docs/free-tools-api.
• Inputs are processed in memory and not stored.

Convert SRT to VTT (or VTT to SRT)

POST https://voicelabs.now/api/tools/srt-to-vtt — the API behind the SRT to VTT converter.

curl -s https://voicelabs.now/api/tools/srt-to-vtt -F file=@subtitles.srt -F download=1 -o subtitles.vtt

The JSON answer is { "output", "format", "cueCount", "warnings" }. warnings lists everything the target format cannot hold and that was therefore removed: SRT <font> and {\an8} tags going to WebVTT; voice, class, language and ruby tags, cue settings and NOTE/STYLE/REGION blocks going to SRT. <b>, <i> and <u> are kept both ways, and every time is copied to the millisecond.

Shift subtitle timing

POST https://voicelabs.now/api/tools/subtitle-timing-shift — the API behind the subtitle timing shift tool.

curl -s https://voicelabs.now/api/tools/subtitle-timing-shift \
  -H 'Content-Type: application/json' \
  -d '{"input":"1\n00:00:05,000 --> 00:00:07,000\nHello","offset_seconds":-1.5}'

A cue that would end before 00:00:00 is removed and one that would start before it starts at 00:00:00; both are counted in warnings. WebVTT inline timestamps (<00:00:01.000>) move with their cue.

Validate SSML

POST https://voicelabs.now/api/tools/ssml-validator — the API behind the SSML validator.

curl -s https://voicelabs.now/api/tools/ssml-validator \
  -H 'Accept: text/markdown' \
  --data-urlencode 'ssml=<speak>Hello <break time="500ms"/> world</speak>'

The JSON answer is { "valid", "errors", "warnings", "elementCount", "textCharacters" }; each error and warning has a line, a column and a message. An invalid document is still a 200 with valid: false. Errors are what XML or the W3C SSML 1.1 Recommendation forbids: an unclosed or mismatched tag, an element in a place it is not allowed, a missing required attribute, or a value outside its grammar (such as time="5" on <break>). Vendor extensions such as <amazon:effect> or <mstts:express-as>, and a <speak> without version, xml:lang or xmlns, are warnings: most engines accept them.

Errors