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

Annotations already establish this is a safe read (readOnlyHint=true, destructiveHint=false), so the description adds value beyond them: an explicit source precedence order, a cost figure ($0.10), an auth requirement (API key), and the anti-fabrication constraint. That is meaningful disclosure for a tool whose annotations only cover safety.

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 and source order are front-loaded, followed by the usage clause and cost/auth note in parentheses. It is dense but every clause carries information; the only minor cost is that the source listing is tightly packed.

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 return shape need not be described. Combined with the usage condition, auth requirement, cost, and source precedence, the description covers what an agent needs to invoke it correctly; the main residual gap is no explicit guidance on when to prefer a sibling retrieval tool instead.

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 100%, so query, fact (alias), and limit (1–20, default 8) are fully documented in the schema itself. The description adds nothing about parameter behavior or the query/fact aliasing, so the baseline 3 applies.

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 states a specific verb and resource ('Return evidence/provenance for a claim') and even enumerates the source hierarchy it walks (polaris_learned_facts, life_events/life_event_relationships, memories), which makes it easy to distinguish from plain retrieval tools like get_memories. It stops short of naming a sibling tool to contrast against, so it is strong but not maximally differentiated.

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?

'Use when the agent must cite why it believes something — do not invent sources' gives an explicit when-to-use condition and a behavioral prohibition. It does not name an alternative tool or state when not to use it, so it lacks the exclusion clause that would push it to a 5.

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