MCP Server Card Auditor

AI Readiness Auditor — validates the MCP Server Card that advertises a remote MCP server for AI clients.

AI Readiness

Makes the site’s MCP server discoverable and connectable by AI clients.

Security

HTTPS-only hosting and browser-safe CORS on the card endpoint.

An MCP Server Card is a static JSON document that describes a remote Model Context Protocol server — its identity, transport endpoints, and protocol versions — so AI clients can discover and connect to it before any protocol exchange. This auditor finds the site’s Server Card, validates the document against the Server Card v1 schema rules, and checks how it is hosted.

How it works

The auditor discovers Server Cards from the audited URL’s origin and then validates every card it finds:

AI Catalog as a link source — fetches /.well-known/ai-catalog.json and follows entries whose type is application/mcp-server-card+json, using their url (fetched with Accept: application/mcp-server-card+json) or inline data. The catalog itself is not audited: a missing, unreachable, or malformed catalog produces no findings, and broken entry links are only recorded as attempts.
Reserved-location fallback — when the catalog yields no card, tries /.well-known/mcp/server-card.json and then /mcp/server-card, stopping at the first HTTP 200.
Document validation — each card is checked against the Server Card v1 schema rules: $schema, name, version, description, and remotes.
Hosting validation — cards fetched over HTTP are additionally checked for media type, CORS, and HTTPS. Inline cards embedded in a catalog entry have no HTTP response of their own, so hosting rules are skipped for them.
Specification pin — every run emits 37A-McpServerCardAuditor-100 (INFORMATION) naming MCP Server Card v1 (27 Jun 2026) and schema.json commit 92999cb3f5d82e648385cb92ce41ed9aa1386eda. That check does not change overall status.

Any failing rule makes the audit FAIL; otherwise a wrong media type produces a WARNING; otherwise the audit is a SUCCESS.

What it audits

Every row maps to one checkRule* method and one CheckCode. Hosting rules (412, 413, 300) are skipped for inline cards embedded in an AI Catalog entry. 37A-McpServerCardAuditor-100 is emitted on every run, including missing-card and invalid-URL failures. CheckCode suffixes use status ranges: 100 information, 200 success, 300–399 warning, 400–499 fail.

CheckCode	Status	When it fires	Recommendation
`37A-McpServerCardAuditor-100`	`INFORMATION`	Every run. Records that this auditor implements MCP Server Card v1 and the pinned `server-card.schema.json` commit.	This auditor implements MCP Server Card v1; documents must set `$schema` to `https://static.modelcontextprotocol.io/schemas/v1/server-card.schema.json`. Schema pin 92999cb3f5d82e648385cb92ce41ed9aa1386eda.
`37A-McpServerCardAuditor-400`	`FAIL`	No Server Card could be obtained from the AI Catalog entries or from either reserved location.	Publish a Server Card at `{origin}/mcp/server-card` or `{origin}/.well-known/mcp/server-card.json`, or list its URL in `{origin}/.well-known/ai-catalog.json`.
`37A-McpServerCardAuditor-401`	`FAIL`	The document served at the card URL cannot be parsed as a JSON object.	Serve a JSON Server Card at `{cardUrl}`.
`37A-McpServerCardAuditor-402`	`FAIL`	The card has no `$schema` field.	Set `$schema` to `https://static.modelcontextprotocol.io/schemas/v1/server-card.schema.json` on `{nameOrUrl}`.
`37A-McpServerCardAuditor-403`	`FAIL`	`$schema` is present but is not the v1 Server Card schema URL (for example a date-versioned or registry schema URL).	Replace `{observed}` with the v1 server-card.schema.json URL.
`37A-McpServerCardAuditor-404`	`FAIL`	The card has no `name` field.	Set name in reverse-DNS form (e.g. `com.example/weather`) on the card at `{cardUrl}`.
`37A-McpServerCardAuditor-405`	`FAIL`	`name` does not match the reverse-DNS `namespace/name` format with exactly one slash.	Change `{name}` to namespace/name, e.g. `com.example/weather`.
`37A-McpServerCardAuditor-406`	`FAIL`	The card has no `version` field.	Set version on `{nameOrUrl}` (e.g. 1.0.0); do not use ranges.
`37A-McpServerCardAuditor-407`	`FAIL`	`version` expresses a range (`^1.2.3`, `~1.2.3`, `>=1.2.3`, `1.x`, `1.*`) instead of a single version.	Replace `{version}` on `{nameOrUrl}` with a single version such as 1.0.0.
`37A-McpServerCardAuditor-408`	`FAIL`	The card has no `description` field (or it is blank).	Add a 1-100 character description to `{nameOrUrl}`.
`37A-McpServerCardAuditor-409`	`FAIL`	`description` is longer than 100 characters.	Shorten the description of `{nameOrUrl}` from `{length}` to at most 100 characters.
`37A-McpServerCardAuditor-410`	`FAIL`	A `remotes[]` entry has a `type` other than `streamable-http` or `sse`.	Set `remotes[{i}].type` on `{nameOrUrl}` to `streamable-http` or `sse` instead of `{observed}`.
`37A-McpServerCardAuditor-411`	`FAIL`	A `remotes[]` entry has a `url` that does not start with `http://`, `https://`, or a `{template-variable}` placeholder.	Change `remotes[{i}].url` on `{nameOrUrl}` from `{observed}` to an http(s) URL or a `{template}` URL.
`37A-McpServerCardAuditor-412`	`FAIL`	The HTTP response serving the card has no `Access-Control-Allow-Origin` header, blocking browser-based clients.	Add `Access-Control-Allow-Origin: *` on `{cardUrl}`.
`37A-McpServerCardAuditor-413`	`FAIL`	The card URL uses the `http` scheme in production (localhost is exempt).	Serve `{cardUrl}` over https instead of http.
`37A-McpServerCardAuditor-300`	`WARNING`	The HTTP response serving the card has a `Content-Type` other than `application/mcp-server-card+json`.	Serve `{cardUrl}` with Content-Type `application/mcp-server-card+json` instead of `{observed}`.
`37A-McpServerCardAuditor-200`	`SUCCESS`	Every rule above passed for a discovered card; one `SUCCESS` check is added per valid card with the message `Server Card "{name}" {version} at "{cardUrl}" is valid.`	—

Output documentation

Status	Description	Test logic
INFORMATION	Provenance only; does not change overall status	Every run includes `37A-McpServerCardAuditor-100` with MCP Server Card v1 and schema commit `92999cb3…` in the message and `Check.data`.
SUCCESS	A Server Card was found, matches the v1 schema rules, and is properly hosted	Card discovered via AI Catalog or a reserved location. Valid JSON object with the v1 `$schema` URL, a reverse-DNS `name`, a single (non-range) `version`, a 1-100 character `description`, and `remotes[]` entries limited to `streamable-http`/`sse` types with http(s) or templated URLs. Fetched cards are served over HTTPS with `Access-Control-Allow-Origin` and the `application/mcp-server-card+json` media type. The specification pin check is still present.
WARNING	The card is valid but served with the wrong media type	`Content-Type` differs from `application/mcp-server-card+json` on an otherwise fully valid card (`300`). The specification pin check is still present.
FAIL	No card was found, the card violates the v1 schema rules, or hosting is unsafe	No card at any discovery location (`400`); invalid JSON (`401`); missing or wrong `$schema` (`402`, `403`); missing or malformed `name` (`404`, `405`); missing or range `version` (`406`, `407`); missing or over-long `description` (`408`, `409`); invalid `remotes[]` type or URL (`410`, `411`); missing `Access-Control-Allow-Origin` (`412`); card served over plain HTTP (`413`). The specification pin check is still present.

Risks and considerations

AI discoverability

Without a Server Card at a discoverable location, AI clients cannot find or auto-configure a connection to the site’s MCP server, so the server is invisible to agentic sessions.
A card that violates the v1 schema (wrong $schema, malformed name, range version) may be rejected by validating clients even when the MCP server itself works.

Client interoperability

Browser-based clients are blocked entirely when the card endpoint lacks Access-Control-Allow-Origin.
Serving the card without the application/mcp-server-card+json media type can break clients that negotiate content via the Accept header.
Invalid remotes[] transport types or endpoint URLs steer clients toward connections that cannot be established.

Security and trust

Server Cards are consumed before the client connects; a card served over plain HTTP can be tampered with in transit and redirect clients to a rogue endpoint.
A stale or inaccurate card (identity, transport, protocol versions) is a confusion or downgrade vector — keep the card consistent with the server’s runtime behavior.

Operational drift

The card is a static document: version bumps, endpoint moves, or transport changes on the server must be mirrored in the card, or clients will act on outdated connection details.

Auditors

AI Readiness

Performance

SEO

MCP Server Card Auditor

AI Readiness

Security

How it works

What it audits

Output documentation

Risks and considerations

AI discoverability

Client interoperability

Security and trust

Operational drift

AI Readiness

Security

​How it works

​What it audits

​Output documentation

​Risks and considerations

​AI discoverability

​Client interoperability

​Security and trust

​Operational drift

How it works

What it audits

Output documentation

Risks and considerations

AI discoverability

Client interoperability

Security and trust

Operational drift