upkeep-mcp

SSL certificate

ssl_check

Read-onlyIdempotent

Inspect a host's TLS certificate to check expiration, issuer, chain trust, hostname coverage, and TLS version. Use it to diagnose browser warnings or plan renewals.

Instructions

Inspects the TLS certificate a host actually serves: when it expires, who issued it, whether the chain verifies, which hostnames it covers, and which TLS version was negotiated.

Use it to answer "when does this certificate need renewing?", "why does the browser warn about this site?" or "does the certificate cover www as well as the bare domain?" — the last being one of the most common real-world misconfigurations, along with a missing intermediate certificate, which is reported as UNABLE_TO_VERIFY_LEAF_SIGNATURE.

Do not use it for domain registration expiry, which is a different date entirely — that is domain_check. It connects to the host but does not request a page; use uptime_check for that.

Certificates that are expired, self-signed or untrusted are inspected and reported rather than refused. Revocation is checked over OCSP, preferring the response a server staples to the handshake and otherwise asking the issuing authority directly; the answer is only believed once its signature verifies against that authority. Many healthy certificates cannot be checked at all, because since 2025 the two largest issuers publish no OCSP responder and distribute revocation by CRL instead — that is reported as an unavailable reason rather than as a problem with the site, and produces no finding. Certificate revocation lists are not downloaded.

A certificate is reported as a warning inside 14 days and as critical inside seven. That window is deliberately shorter than the one domain_check uses for registrations: ACME clients renew with 30 days left, so 28 days remaining is a healthy site in the middle of a normal renewal, not a problem. Returns findings ordered by urgency, worst first.

Input Schema

TableJSON Schema

Name	Required	Description	Default
`port`	No	TCP port to connect to. Defaults to 443. Use 8443, 993 and so on for other services.
`domain`	Yes	The host whose certificate should be inspected, e.g. "example.com" — no scheme, no trailing slash. A full URL is also accepted and reduced to its hostname. The certificate is read for exactly this host, so "www.example.com" and "example.com" are different checks.

Output Schema

TableJSON Schema

Name	Required	Description
`tls`	Yes	What the handshake negotiated.
`host`	Yes	The host that was contacted, in ASCII (punycode) form.
`port`	Yes	The port that was contacted.
`chain`	Yes	The certificate chain and whether it verified.
`issuer`	Yes	Issuer common name, e.g. "R11" or "GTS CA 1P5".
`subject`	Yes	Subject common name.
`coverage`	Yes	Which hostnames this certificate is valid for.
`findings`	Yes	What needs attention, worst first.
`issuedAt`	Yes	Start of the certificate validity, ISO 8601 UTC.
`severity`	Yes	How much attention this needs. "critical" means act now; "warning" means act this month; "unknown" means the check could not establish the fact, which is not the same as it being fine.
`checkedAt`	Yes	When the check ran, ISO 8601 in UTC.
`expiresAt`	Yes	When the certificate expires, ISO 8601 UTC.
`revocation`	Yes	Whether the certificate has been revoked, and how confidently that was established.
`serialNumber`	Yes	Certificate serial number, hexadecimal.
`daysUntilExpiry`	Yes	Whole days until the certificate expires, negative if already expired. Floored, so a certificate expiring in a few hours reads as 0.
`fingerprintSha256`	Yes	SHA-256 fingerprint of the certificate.

Schema Changelog

Changes observed during successful MCP inspections.

First observedv0.6.1Oct 5, 2026

TDQS

A4.6/5.0

Behavior5/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations only cover the safety profile (readOnly/idempotent/non-destructive); the description goes well beyond them. It discloses that expired/self-signed/untrusted certs are inspected rather than refused, how OCSP revocation is verified, that CRL lists are not downloaded, how unverifiable certs are reported with no finding, and the exact 14-day/7-day severity windows.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Front-loads purpose before routing guidance, and the sequencing (what it does → when to use → when not to use → behavior) is clean. It is longer than strictly needed for tool selection — the OCSP/CRL paragraph is dense — but every claim defends against a plausible misinterpretation, so little is wasted.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness5/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

An output schema exists, so return values need no explanation, and the description fills the remaining gaps: severity thresholds, ordering (worst first), and the deliberate divergence from domain_check's renewal window. Nothing an agent needs to call or interpret this tool is missing.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, so both parameters are already fully documented in the schema. The description adds no port guidance and only echoes the schema's note that www and bare domain are distinct checks. Baseline 3 is appropriate when the schema carries parameter meaning.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

Opens with a specific verb+resource ('Inspects the TLS certificate a host actually serves') and enumerates exactly what it reports: expiry, issuer, chain verification, covered hostnames, negotiated TLS version. It explicitly distinguishes itself from sibling tools domain_check and uptime_check, so an agent can route correctly without opening a schema.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines5/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

Gives concrete use-case phrasings ('when does this certificate need renewing?'), names the two most likely alternative tools with the condition that selects them (domain_check for registration expiry, uptime_check for page requests), and explicitly states 'Do not use it for...'. Both when-to-use and when-not-to-use are covered.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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