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

Annotations already declare readOnlyHint=true, so the safety profile is covered. The description adds meaningful behavioral context: the rules are persistent, auto-classify future events, and skipping review is a consequence of the learned map. It also clarifies the direction field semantics (inbound/outbound/null = both), which is beyond what annotations provide. Minor gap: no mention of pagination or ordering, but not critical for a list tool.

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 sentences, each earning its place: the first defines the resource and its purpose, the second enumerates the returned fields, and the third routes to sibling tools. Information is front-loaded and there is zero 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?

The tool is a simple read-only list with one optional parameter, a rich output schema, and full schema coverage. The description explains the domain significance (learned vendor map, skip review), the returned fields, and the modification alternatives. Nothing an agent needs to call it correctly is missing.

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 coverage is 100% and the single parameter org_id is fully documented in the schema, including its default and the fact that it can be omitted. The description reinforces this by saying 'you normally omit it and never need to ask the user for their organisation UUID' — adding practical guidance beyond the schema. Baseline 3 is exceeded because the description adds real usage nuance.

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 ('Lists') and resource ('the org's persistent counterparty rules'), and immediately distinguishes it from sibling tools by explaining what the rules do (auto-classify future events so they skip review). It also names sibling tools update_counterparty_rule and delete_counterparty_rule, making the purpose unmistakable.

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?

The description explicitly says when to use this tool (to view the learned vendor map) and names the alternatives for modifying rules (update_counterparty_rule, delete_counterparty_rule), noting they affect future classification only. This gives clear routing guidance without needing to inspect sibling schemas.

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