Calibrated probabilities
Not a thumbs-up classifier. A calibrated model score plus bounded content evidence lets you pick the review threshold that matches your false-positive tolerance.
spam classification · v1
Stop spam
at the API.
Updated August 22, 2026
Drop in one endpoint. Get a probability back.
No queues. No models to host. No surprises.
10,000 requests/month free · no credit card · two-line install
curl -sX POST https://api.siftfy.io/v1/predict \
-H "X-API-Key: $SIFTFY_KEY" \
-H "Content-Type: application/json" \
-d '{"text": "FREE iPhone! click http://bit.ly/x to claim NOW"}'
# {
# "spam_probability": 0.65,
# "likelihood": "medium",
# "max_confidence": 0.84
# }89.2%
F1 on 1,956 comments
<10ms
p99 latency, CPU only
1
endpoint to learn
18MB
model · BERT-tiny + signals
How it works
01
Create a key
Sign in with your email — we send a one-time link. Generate an API key from the dashboard.
02
Send a request
POST any text to /v1/predict. The response is a calibrated spam score between 0 and 1.
03
Threshold & ship
Use max_confidence when setting policy. The model alone cannot reach the 0.85 block band.
Built for an inbox that doesn't wait.
Single round trip
No queues, no async webhooks, no streaming. One HTTPS request, single-digit milliseconds, response inline.
Per-key everything
Every key has its own usage counter, last-used timestamp, and revocation. Issue keys to specific apps; revoke any one of them in a click.
Deterministic by design
Model version is pinned per release. Same input, same probability — no silent drift on your spam filter when we retrain.
In production in our own products
Both are operated by VectraSEO LLC, the company that operates Siftfy. They are shown here as working integrations we run ourselves, not as third-party endorsements.
Frequently asked questions
- How accurate is the model?
- On an independent 1,956-comment evaluation, the current model and bounded content signals achieved 89.2% F1, 96.6% precision, and 82.8% recall. Validate the returned scores against your own traffic before enforcing a policy.
- What language(s) does it support?
- The active model is trained primarily on English. Non-English inputs still classify, but accuracy degrades. If you need a specific language we can swap the underlying model — email us.
- How fast is /v1/predict?
- Single-digit milliseconds for SMS-length text on CPU. Most calls round-trip in under 10ms p99 from the same region. There are no async queues, no webhooks — one HTTP request, one response.
- Do you store the text I send?
- No. We log request metadata (timestamp, status, duration, tenant id) but the request body is not persisted. If you need contractual confirmation in writing, get in touch.
- What happens if I exceed my quota?
- On the free tier you get 10,000 requests/month and 60/minute. Cross either and the API returns 429 with a Retry-After hint. Pro lifts the cap to 1M/month included plus $0.0001/req metered.
- Can I self-host?
- We run a managed service. For very large volumes or air-gapped requirements we can talk about a dedicated deployment — email hi@siftfy.io.
Drop it in where you already are.
Eight integrations, each with a real runnable example. Pick the one that matches your stack — or read the /v1/predict reference and roll your own in 15 lines.
- Contact formsServer-side classification per submission. No CAPTCHA, no honeypot.
- CommentsScore every new comment on a calibrated 0-1 axis before it goes live.
- SignupsCatch fake-account registrations on the natural-language fields.
- CAPTCHA alternativesReplace reCAPTCHA friction with one server-side call. Same protection, no UX tax.
- WebflowFront Webflow's form-submission webhook with a 30-line worker.
- Ghost CMSFilter spam member signups via Ghost's webhook + Admin API.
- Static sitesAstro, Next.js, Gatsby, SvelteKit — one serverless function does it.
- Headless CMSSanity, Contentful, Strapi — generic webhook pattern, per-type field mapping.
Two lines from now,
you're filtering spam.
10,000 free requests every month. Pro is $9 + $0.0001 per request after that.