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

Annotations declare destructiveHint=true and idempotentHint=false but carry no operational detail. The description adds rich behavior: empty fields are preserved, bid_price auto-switches to manual bidding, TikTok silently ignores bid without bid_type, confirm=false previews. This is exactly the beyond-annotation context most definitions omit.

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-loaded with purpose and the key 'why', followed by dense parameter semantics. Every sentence earns its place, though the density is high and could benefit from light formatting. No filler or repetition.

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 15-param mutation tool with 0% schema coverage and no param enums, the description supplies format, enums, defaults behavior, preview mode, and the critical bid_type coupling. Output schema exists, so return values need not be described. Complete for the calling decision.

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%, so the description carries the full burden. It explains format for comma-separated ID lists, the 'YYYY-MM-DD HH:MM:SS' schedule format, pacing enum values (PACING_MODE_SMOOTH/FAST) with semantics, bid_type interplay, and the empty-string-means-unchanged convention. This compensates completely for the zero schema coverage.

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 (updates) and resource (TikTok ad group targeting, bid, schedule) with exact scope. Explicitly contrasts with what was previously possible ('only status and budget could be changed') and distinguishes itself from siblings like update_tiktok_adgroup_status and update_tiktok_adgroup_budget.

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?

Provides explicit when-to-use ('widen/narrow locations, ages, genders... change the bid, or extend run dates') and the critical motivation (avoid resetting learning phase). Names the alternative approach (deleting and rebuilding) and why it's worse.

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