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

Goes well beyond the annotations (readOnlyHint=false, destructiveHint=false, openWorldHint=true) by disclosing the read-modify-rewrite mechanism, the guarantee that name/email/password are untouched, and the mandatory two-phase confirmation. It stops short of noting any rate limits, auth requirements, or what happens on partial failure.

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?

Front-loads the action, then the mechanism, then the confirmation flow in three tight sentences with no filler. Slightly dense in the confirmation sentence but every clause carries operational information.

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 mutation tool with no output schema, it covers the safety profile, the mutation semantics, and the return preview ('preview shows the resulting opt-in state'). An agent has everything needed to invoke it correctly in either client mode.

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 schema itself already documents each opt-in flag and the confirmToken's role in detail, so the description's parameter contribution is marginal. Baseline 3 applies when the schema does the heavy lifting; the description reinforces but does not extend it.

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 and resource (turn the account's email opt-ins on/off) and enumerates the exact fields affected (news, artist activity, promos). This is clearly distinguishable from all siblings, which are read/download/comment operations.

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?

Explicitly describes the when and how: confirmation is required first, with a named fallback path (preview + confirmToken) for clients lacking elicitation, and states that confirmToken is passed only after user approval, never on the first call. The condition selecting each branch is spelled out rather than implied.

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