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

Annotations already flag a non-read-only, destructive, open-world mutation, but the description adds real behavior the annotations cannot: bids are rounded to whole micros, bids on Smart Bidding campaigns are stored but unused in serving, and an invalid amount returns {'error': 'invalid_amount'} with nothing changed. It does not mention permission requirements or rate limits, but the safety-relevant semantics are well covered.

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?

Four dense sentences, front-loaded with the mutation, then the conditional caveat, then the validation rule, then the workspace parameter. Nothing is padded, though the inline error-JSON fragment and the mixed German/English naming cost a little parsing speed for an English-speaking agent.

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 three-parameter mutation with an output schema, the description covers the effective scope (bidding strategy), the unit and rounding, the validation failure mode and workspace scoping. Nothing an agent needs to call this 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 description coverage is 0%, so the description must carry the load, and it does for two of three parameters: cpc_bid_eur is defined by currency, rounding, the >0 constraint and the exact failure mode; workspace is defined as a client slug that is optional when only one workspace exists. ad_group_id is left entirely to the schema, which is the only real gap.

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: change the CPC bid of an ad group, plus the unit (EUR, rounded to whole micros). This inherently separates it from ads_update_keyword_bid, ads_update_campaign_budget and ads_update_ad_group_name/status, so an agent can pick the right mutation without opening the schema.

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?

Gives a strong conditional: it only takes effect on MANUAL_CPC campaigns, and points the agent to bidding_strategy via ads_list_campaigns to check first. It does not name sibling tools to use instead (e.g. keyword-bid vs ad-group-bid), so it stops just short of full routing guidance.

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