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

Annotations already declare readOnlyHint=false and destructiveHint=false, and the description adds real substance beyond that: hard input bounds (64 KiB, 2000 lines, 4096 chars/line), explicit non-behaviors (no model calls, no repo fetching, no code execution), and the nature of the response (a redacted signed receipt). The non-readonly hint is consistent with producing a signed receipt artifact rather than contradicting the text. It stops short of 5 because the 'verified fixed-order session' requirement is stated opaquely rather than explained.

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?

The purpose is front-loaded in the first clause, followed by preconditions and then limits, with no filler sentences. Density is high but several tokens ('$1', 'VulnCanon', 'checkout caller') are undefined jargon that cost clarity rather than word count.

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?

An output schema exists, so the description need not explain return values, and the mention of a redacted signed receipt is a useful bonus. For a tool with three undocumented parameters, a mutation-adjacent annotation profile, and four similar security siblings, however, the missing parameter meanings and sibling routing make it only minimally complete.

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% across three parameters, so the description must carry the full burden and largely fails to. 'The checkout caller and verified fixed-order session' gestures at agent_id/session_id but does not say which parameter maps to what, whether session_id is optional, or what 'source' should contain. An agent still cannot construct a valid call from this text plus the bare schema.

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?

The description gives a specific verb and resource ('inline VulnCanon source scan') plus a scope caveat ('indicators, not proven exploits') that sets expectations about output quality. It is distinguishable from siblings like screen_injection and security_preflight by being an inline source scan rather than a preflight or injection screen. Jargon ('$1', 'VulnCanon', 'fixed-order session') keeps it short of a 5.

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?

A prerequisite is stated ('Direct MCP requires the checkout caller and verified fixed-order session'), which implies when the tool can be invoked. However, there is no explicit guidance on when to choose this over screen_injection or security_preflight, and no when-not-to-use condition is given. The agent must infer routing from the sibling names alone.

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