# ProbeKit

> Checks and diagnostics for developers and AI agents: mail authentication (SPF, DMARC, DKIM, MX) and DNS, with structured results and explained findings.

## Tools

- [DNS lookup](https://probekit.dev/tools/dns/dns-lookup): Resolve A, AAAA, CNAME, MX, NS, TXT, SOA, CAA and SRV records for a name, with TTL and the public resolver that answered.
- [DKIM record check](https://probekit.dev/tools/mail/dkim-check): Check the DKIM public key record for a domain and selector: key type, RSA key size, revoked keys, testing mode and multiple records.
- [DMARC check](https://probekit.dev/tools/mail/dmarc-check): Look up and explain a domain's DMARC record: policy, subdomain policy, percentage, report addresses and inheritance from the organisational domain.
- [Mail configuration check](https://probekit.dev/tools/mail/mail-check): One report on a domain's mail DNS: MX, SPF and DMARC together, plus DKIM for the selectors you supply. Bulk checks of up to 20 domains.
- [MX lookup](https://probekit.dev/tools/mail/mx-lookup): List a domain's mail servers sorted by preference, with resolved addresses, null MX detection and warnings for MX targets that do not resolve.
- [SPF check](https://probekit.dev/tools/mail/spf-check): Check a domain's SPF record: DNS lookup count against the limit of ten, include and redirect chains, loops, multiple records and permissive all.

## Guides

- [Guides: email authentication explained](https://probekit.dev/guides): Plain-language guides to SPF, DMARC, DKIM and MX, written from the RFCs, with links to the matching checks and the findings they can report.
- [DKIM explained: selectors, keys and rotation](https://probekit.dev/guides/dkim): How DKIM signing and key records work under RFC 6376: selectors, the v, k, p and t tags, key sizes after RFC 8301, Ed25519, rotation and revocation.
- [DMARC explained: policy, alignment and reports](https://probekit.dev/guides/dmarc): How DMARC works under RFC 7489: alignment with SPF and DKIM, the p, sp and pct tags, report addresses, and how to move from none to reject safely.
- [MX records explained: priority and null MX](https://probekit.dev/guides/mx): How MX records route email under RFC 5321: preference values, fallback to the address record, null MX from RFC 7505, valid targets and common mistakes.
- [SPF explained: lookups, includes and all](https://probekit.dev/guides/spf): How an SPF record works under RFC 7208: mechanisms, qualifiers, the ten-lookup and two-void-lookup limits, include versus redirect, and common mistakes.

## Docs

- [Bulk checks](https://probekit.dev/docs/bulk): Check up to 20 domains in one request: the JSON format, how results keep their order, how duplicates are counted and how the price is calculated.
- [Errors and status codes](https://probekit.dev/docs/errors): The HTTP status codes of the public ProbeKit API, what each one means, whether a payment is taken, and the common error body with the request id.
- [Freshness and caching](https://probekit.dev/docs/freshness): How to read observed_at, fresh_until, cache_hit and resolver in the meta of a response, and why two calls can return different answers.
- [Payments with x402](https://probekit.dev/docs/payments): How paying per request with x402 works: a 402 Payment Required answer, the price in advance, payment in USDC on Base, then the same request again.
- [Quickstart](https://probekit.dev/docs/quickstart): Start using ProbeKit checks: what a request looks like, what comes back, and how errors and freshness are reported in every response.

## API

- [API reference: paid mail and DNS checks](https://probekit.dev/docs/api): Reference for the ProbeKit API: every endpoint with method, URL, price, input, example requests in curl, Python and JavaScript, responses and errors.
- [DNS lookup API](https://probekit.dev/docs/api/dns-lookup): GET /v1/dns/lookup: Resolve selected record types with TTL and the resolver that answered. Price, input fields, example requests, responses and errors.
- [Mail configuration check API](https://probekit.dev/docs/api/mail-check): GET /v1/mail/check: One report covering MX, SPF, DMARC and DKIM for known selectors. Price, input fields, example requests, responses and errors.
- [Bulk mail configuration check API](https://probekit.dev/docs/api/mail-check-bulk): POST /v1/mail/check/bulk: Run the mail configuration check on up to 20 domains in one request. Price, input fields, example requests, responses and errors.
- [Free retry of failed bulk items API](https://probekit.dev/docs/api/mail-check-bulk-retry): POST /v1/mail/check/bulk/retry: Run the items of a paid bulk request that failed for technical reasons again, free of charge. Rules, input, example request…
- [DKIM record check API](https://probekit.dev/docs/api/mail-dkim): GET /v1/mail/dkim: Check the DKIM public key record for a given selector. Price, input fields, example requests, responses and errors.
- [DMARC check API](https://probekit.dev/docs/api/mail-dmarc): GET /v1/mail/dmarc: Look up and explain a domain's DMARC policy and tags. Price, input fields, example requests, responses and errors.
- [MX lookup API](https://probekit.dev/docs/api/mail-mx): GET /v1/mail/mx: List a domain's mail servers with priorities, including null MX. Price, input fields, example requests, responses and errors.
- [SPF check API](https://probekit.dev/docs/api/mail-spf): GET /v1/mail/spf: Parse and evaluate a domain's SPF policy, including the DNS lookup budget. Price, input fields, example requests, responses and errors.
- [OpenAPI 3.1 document](https://probekit.dev/openapi.json): Machine-readable description of every endpoint, price and error.
- [SKILL.md](https://probekit.dev/SKILL.md): Instructions for AI agents: choosing a tool, paying with x402 and reading results.

## Reference

- [Findings reference](https://probekit.dev/findings): Every finding code ProbeKit can report, grouped by topic, with what it means, why it matters and what to do about it.
- [Pricing](https://probekit.dev/pricing): Fixed prices per check and per-item prices for bulk requests, known before you pay. No account, no subscription; pay per request with x402 in USDC.
- [Tool catalog: mail and DNS checks](https://probekit.dev/tools): All ProbeKit tools for email authentication and DNS: SPF, DMARC, DKIM, MX, a combined mail report and DNS lookups, with prices and limits.