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

While annotations already indicate a non-read-only operation (readOnlyHint=false), the description adds meaningful behavioral context: activation 'start[s] serving' and requires a creative to be submitted first. The output_format also specifies the return value ('Activated media buy with won_at timestamp'), providing transparency beyond the annotations. It does not contradict any annotations.

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 description is efficiently structured into short labeled sections (tool_description, when_to_use, combination_hints, output_format), with no wasted words. Every section adds distinct value and is easy to scan.

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 simple mutation tool with one parameter and no output schema, the description is complete: it explains what the tool does, when to use it, what must happen before, what happens after, and what the response will be. The combination_hints also integrate it into the broader workflow, covering the tool's context comprehensively.

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?

The single parameter media_buy_id is fully documented in the input schema (100% coverage), including its type and description. The tool description does not add further parameter-specific details beyond what the schema already provides, so baseline 3 is appropriate.

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 action: 'Activate an approved media buy to start serving.' It clearly identifies the verb (activate), resource (media buy), and the intended effect, effectively distinguishing it from sibling tools like pause, cancel, and submit_creatives.

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 'when_to_use' section explicitly states 'After submit_creatives, when ready to go live with the campaign,' and the description notes the prerequisite 'Requires creative to be submitted first.' The combination_hints further clarify the sequence and mention alternatives (pause, cancel), making usage guidance explicit.

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