WhoisXML API sells SSL certificate queries from $15 a month for 1,000, and 1Lookup reads a certificate for $0.010 and returns the verdict and the days left.

Getting the SSL certificate of a domain by API. The product page says 'We provide access to the latest SSL certificate issued for every domain'. A request is a GET with an apiKey and a domainName, plus optional withChain, hardRefresh and outputFormat (JSON or XML) parameters.

Prepaid queries in eight tiers from 1,000 to 800,000, bought three ways. One-time: 1,000 queries $17, 5,000 $79, 10,000 $119, 50,000 $399, 100,000 $529, 200,000 $749, 400,000 $1,099 and 800,000 $1,549, and the page says 'Credits do not expire'. Monthly: $15, $69, $99, $319, $449, $629, $899 and $1,249 for the same tiers, and unused monthly credits do not roll over. A yearly subscription lists the same tiers from $150, and a free plan gives 100 queries with no credit card. Prices checked October 2026.

2 credits per certificate read, free when the domain has no certificate to read. On the Starter plan ($99 a month for 20,000 credits) a check is about $0.010, which covers 10,000 certificates a month and is $9.90 per 1,000. At the Enterprise end of the rate card it is about $0.004. WhoisXML API is the cheaper bill at small monthly volumes: $15 for 1,000 queries and $69 for 5,000, against $99 for a Starter month.

It depends on volume. For 1,000 certificates a month WhoisXML API is cheaper in total ($15 a month, or $17 one-time), and so it is for 5,000 ($69 a month). At 10,000 a month the two cost the same: $99 on WhoisXML API's monthly tier, and $99 for a Starter month. At its larger tiers WhoisXML API's printed price per 1,000 keeps falling, to $1.56 at 800,000 a month, which is below 1Lookup's $4.00 at the Enterprise end of the rate card. One-time credits do not expire, so for an occasional large batch that is the cheaper way too.

The certificate's own detail: validFrom and validTo, serial number, signature algorithm, subject and issuer distinguished names, the PEM, public key type and bits, and extensions such as subjectAlternativeNames, keyUsage, CRL distribution points and OCSP endpoints. With withChain=1 it returns every certificate from the end-user certificate to the root, each marked end-user, intermediate or root, with a validation type (domain, organization, extended, individual, self-signed or self-signed-ca). 1Lookup returns the verdict and the facts that decide it, and the chain with each certificate's subject, issuer and end date.

Its output-format page lists the certificate fields (validFrom, validTo, validationType, subject, issuer, publicKey type and bits, extensions) with no verdict, days-left, hostname-match or trust field among them, so a caller works those out from the fields. 1Lookup returns certificate_status, days_remaining, hostname_matches and trusted ready to use, with each problem as a sentence.

WhoisXML API's request has a hardRefresh option ('1 results in getting fresh data', default 0), and each result's auditCreated is 'the date (UTC) when the certificate was collected from the server'. 1Lookup makes a new connection to the domain for every request that is not answered from the cache, and shows the day it did so in checked_at. The same domain asked again within a day by the same user is answered from the cache at no charge, and bypass_cache: true reads it again.

Its error-codes page lists 408 Request Timeout, which 'may also appear if the API cannot connect to the target domain name or IP address', and 403 Forbidden, which covers low credits, a wrong API key or an IP not on the allowlist. 1Lookup answers 503 with a Retry-After header when a connection does not finish, and does not charge for it.

On price at small and large volumes, and on raw detail. Its smallest monthly tier is $15, its printed tiers fall to $1.56 per 1,000 at 800,000 a month, one-time credits do not expire, and it returns the PEM, the extensions, the CRL and OCSP endpoints and the chain with validation types. It also lists WXA.ONE ('one balance that works across our product portfolio', from $129 a month) for spending one balance across its other products. 1Lookup charges per certificate read and returns a verdict.

If you want the raw certificate fields for many domains at the lowest price per query, WhoisXML API is the stronger buy. If you want the certificate already judged, with the days left, a name match and a verdict in plain words, bulk CSV files and one balance that also pays for phone, email and IP checks, 1Lookup's SSL Certificate Check bills 2 credits only when a certificate is read.

If you want certificate detail such as the PEM or the extensions, or very large volumes at a low printed price, yes. If you want a verdict and the days left without writing the checks yourself, compare the tier you would buy with a price per certificate read.