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

Annotations are weak (all mutation hints false), and the description adds real behavioral context beyond them: hard limits (64 KiB, 2000 lines, 4096 chars/line), explicit exclusions (no model calls, no repository fetching, no code execution), and the return artifact (redacted signed receipt). It stops short of explaining why readOnlyHint is false, i.e., what state the session requirement mutates.

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

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

Three short sentences, front-loaded with the core purpose and limits. The middle sentence about 'checkout caller' and 'fixed-order session' is cryptic but earns its place as a prerequisite note; no filler.

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

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

With an output schema present, the return contract need not be spelled out, and the description adequately conveys the operation's bounds and side-effect exclusions. However, for a tool with 0% parameter coverage, the complete absence of parameter guidance leaves a real gap for correct invocation.

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

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

Schema description coverage is 0% and none of the three parameters (source, agent_id, session_id) are described. The vague mention of 'checkout caller' and 'verified fixed-order session' gestures at the session/auth inputs but does not tell the agent what agent_id or session_id should contain, so the description fails to compensate for the coverage gap.

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

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

States a specific verb (scan) and resource (inline VulnCanon source) with a clear scope qualifier ('$1 bounded', 'indicators, not proven exploits'). The term 'VulnCanon' is unexplained jargon, but the verb+resource pairing is unambiguous and distinguishes it from the other security-oriented siblings.

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

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

'Direct MCP requires the checkout caller and verified fixed-order session' implies a prerequisite context, but it never states when to choose scan_source over screen_injection, security_preflight, or get_security_receipt. Usage is implied rather than routed.

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