# Spaw vs Kickbox: email verification API comparison

How Spaw and Kickbox compare on pricing, billing rules, verification depth and limits, from Kickbox's public pages checked on 2026-09-03. Corrections: support@spaw.co.

| | Spaw | Kickbox |
| --- | --- | --- |
| Pricing model | Pay-as-you-go credit packs bought through Stripe Checkout; no subscription, credits never expire | not published |
| Free tier | 10 free credits every month, no card required | not published |
| Price per 1,000 at about 10k | $7.80 (Growth pack: 5,000 credits for $39) | not published |
| Price per 1,000 at about 100k | $4.99 (Volume pack: 100,000 credits for $499) | not published |
| Unknown or catch-all results billed | Yes, by verdict: a deliverable or risky answer costs 1 credit even when the mailbox is unconfirmed; the automatic re-checks are free | not published |
| Undeliverable results billed | No, undeliverable verdicts are always free | not published |
| SMTP mailbox check | Yes | not published |
| Catch-all handling | A catch-all answer is remembered per domain for 7 days, and every unconfirmed mailbox carries a published 0 to 100 mailbox_confidence estimate | Results are deliverable, undeliverable, risky or unknown; how accept-all domains are billed is not published on the pages we could read |
| Bulk limit | 100,000 addresses per bulk job, with an HMAC-signed completion webhook | not published |
| Batch API | 50 addresses per synchronous request, probes sent concurrently | not published |
| Rate limit | 5 requests per second per key | not published |
| Official SDKs | Python, Node.js, PHP | PHP, Node.js, Ruby, Python |
| Data retention | Lookup history kept for 30 days, then pruned; test addresses are never logged | not published |

## When Kickbox fits better

Teams that want a single quality score next to the verdict and already build on one of Kickbox's four official libraries.

- Sendex score: a quality estimate between 0 (no quality) and 1 (perfect quality)
- Four official client libraries on GitHub

## When Spaw fits better

Developers who want one flat price per answered lookup, a transparent risk score, and an API that documents every field.

- Kickbox's website blocked automated reading when we checked, so its prices are not reproduced here; Spaw's packs and free grant are listed at spaw.co/pricing
- Spaw's risk score is a 0 to 100 sum of published weights; Kickbox's Sendex score is a 0 to 1 quality estimate
- Both report deliverable, undeliverable, risky and unknown-style outcomes; Spaw adds a machine-readable reason and 27 named fields per address
- Spaw bills nothing for undeliverable verdicts and repeats within 7 days

## Questions

**Does Spaw charge for catch-all or unknown results?** Spaw bills per answer, not per probe outcome: a lookup that comes back deliverable or risky costs 1 credit even when the mailbox could not be confirmed, for example on a catch-all domain or after greylisting. Undeliverable verdicts, invalid input, repeats within 7 days and the automatic re-checks behind callback_url are free. Kickbox does not publish how it bills them.

**Can I move a list from Kickbox to Spaw?** Yes. Upload the CSV to the dashboard or POST it to the bulk endpoint; Spaw keeps your columns, adds the verdict columns, and lets you download only the deliverable, risky or undeliverable rows. Addresses that come back undeliverable join your suppression list so later runs skip them for free.

**Is there a free tier?** Every Spaw account receives 10 free credits at the start of each month with no card on file, and unused credits accumulate. Kickbox does not publish a free tier on the pages checked.

## Sources (checked 2026-09-03)

- [Kickbox GitHub organization](https://github.com/kickboxio)
- [Kickbox Python client README](https://github.com/kickboxio/kickbox-python)

Kickbox is a trademark of its owner. Spaw is not affiliated with it.

Reference: https://spaw.co/compare/kickbox