MCP-SEC-006

Schema depth and subschema count stay within safe bounds

“Implementations SHOULD apply reasonable bounds, such as a maximum schema depth, a cap on the total number of subschemas, or a per-validation time budget, to prevent a malicious schema from acting as a Denial-of-Service vector.” — spec anchor

How to fix this

Keep advertised schemas shallow and bounded in subschema count. The specification asks for reasonable limits without naming a number, because a deeply nested schema is a denial-of-service vector against whatever validates it.

How the validator checks this

Probe P2.1, against a streamable-http server on the modern protocol. What it reports:

pass: Schemas stay within the bounds this validator applies: depth … of …, … subschemas of
warn: …. The specification asks for "reasonable bounds" without naming a number, so these are this validator's limits, not a spec threshold.

Quoted from the probe that runs this check, so it cannot drift from what the validator actually reports.

This rule is checked deterministically: a fail here is a certain violation, not an inference.

Checked in the same request as MCP-HDR-008, MCP-HDR-009, MCP-RES-003, MCP-RES-006, MCP-RES-007, MCP-ERR-003, MCP-ERR-004, MCP-ERR-005, MCP-ERR-008, MCP-CAC-001, MCP-CAC-002, MCP-CAC-003, MCP-CAC-004, MCP-CAC-005, MCP-SCH-001, MCP-SCH-002, MCP-SCH-003, MCP-SCH-004, MCP-SCH-005, MCP-SCH-006, MCP-SCH-007, MCP-SEC-004, MCP-SEC-005, MCP-DEP-005.

Check your own server against this rule

The validator makes real protocol requests and reports this rule as pass, warn or fail alongside the other 78. Validate a server or read how the check works.

Schema depth and subschema count stay within safe bounds

How to fix this

How the validator checks this

Check your own server against this rule

Other Security posture rules