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fetch.li
Get a key

Spark

For a caption, an image alt line, or a short client brief when you already hold the facts. Start with Getting started. Pricing for a key is on pricing. The free deterministic line is caption. Vibe labels stay on vibe, which is a different model and a different job.

POST /v1/spark needs an API key. It is not on the free demo. It does not browse the web. It does not fetch a URL. It is not an MCP tool.

Send JSON:

{ "task": "caption", "facts": "Market day in the square", "tone": "people" }

task is caption, alt, or brief. tone is optional: people, maker, or client. facts is 1 to 2000 characters. Extra keys are refused, so you cannot pass a model name or a system prompt.

The draft may only use numbers that already appear in facts. If it adds a number, the answer is dropped, available is false, and the draft is not returned. Check the line before you publish. This host does not store a chat.

If XAI_API_KEY is not set, the route returns 503. It does not invent a sentence.

Parameters

Name Required Notes
task yes caption, alt, or brief
facts yes The only source
tone no people, maker, or client

Related

Caption for the free line. Auth for the Bearer key.

Getting startedUse Try buttons without an account, then get an API key when you need vibe classification or higher limits. Answer contractEvery success body leads with ok, answer, and say. format=text, md, svg, csv. pricing Vibe classifyClassify marketing copy into a primary vibe, mood tags, and a five-colour palette using AI. Spreadsheets and no-codeFirst fetch.li call, then Google Sheets, Zapier, Make, and the jobs the API is actually good at. Demo tierWhat you get for free on GET endpoints, the 60 calls per hour limit, and what requires a paid key.