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

Annotations already establish this is a non-read-only, non-idempotent, non-destructive write, and the description adds the prerequisite relationship to campaigns plus a unit caveat on amount. It does not warn about the practical consequence of idempotentHint=false (retrying on an ambiguous failure can create a duplicate budget), which is the main behavioral risk here.

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?

Two short sentences, front-loaded with the action and immediately followed by the workflow constraint. No filler, and the amount-unit note is a brief, high-value caveat.

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 6-param write tool with full schema coverage and no output schema, the description supplies the key missing context (prerequisite ordering, units). It omits what a created budget looks like in the response and whether the shared-budget flag changes behavior for future campaigns, but those are secondary.

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% and each parameter (including validateOnly, extraFields, explicitlyShared) is well documented inline, so the baseline is 3. The description only restates the 'account currency, not micros' point already present in the amount schema, adding no new semantics.

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 ('Create a shared daily campaign budget') and immediately clarifies its position among siblings: it is a prerequisite for create_campaign and distinct from update_campaign_budget. An agent can place it in the workflow without opening a 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 explicit sequencing guidance ('a campaign cannot be created without one, so this is normally the first write call'), which routes the agent correctly relative to create_campaign and update_campaign_budget. It stops short of naming alternatives or stating when not to call it (e.g., if a budget already exists).

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