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

Annotations already indicate readOnlyHint=false, destructiveHint=false, and idempotentHint=false. The description adds valuable behavioral context: the new leg starts empty, one leg per ruleset with 409 on conflict, and permission requirements (403 for ordinary players). It doesn't contradict annotations. It could mention what the response contains, but the output schema exists.

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: what the tool does, what the new leg starts as, and the key constraints (one leg per ruleset, permissions). Front-loaded with the core action and resource.

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?

For a 2-parameter tool with 100% schema coverage, an output schema, and annotations covering safety, the description is complete. It explains the concept of a leg, the empty start state, the uniqueness constraint, and permission requirements. An agent has everything needed to select and invoke this tool correctly.

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 the schema already documents both parameters. The description adds context about the ruleset parameter's uniqueness constraint (409 if leg exists) and clarifies that campaignId is the target campaign. This goes slightly beyond the schema, but the schema already carries most of the burden.

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 clearly states the verb ('Add'), the resource ('a new active leg to a campaign'), and the specific purpose ('letting the same campaign also run under that ruleset'). It distinguishes itself from sibling tools like play_set_campaign_leg_active and the other play_add_campaign_* tools by explaining what a leg is and that it starts empty.

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 add a leg for a ruleset), what the new leg starts as, and the constraint 'One leg per ruleset' with the 409 behavior. It also states who can call it (campaign owner or accepted gamemaster) and that ordinary players get 403, which is clear usage guidance.

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