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

Annotations declare destructiveHint=true and idempotentHint=true, but the description adds the non-obvious behavioral context: changes are staged and never published, unspecified fields are preserved, concurrent edits are refused rather than overwritten, and parameter entries replace same-key entries. These are exactly the mutation semantics an agent needs beyond the hint flags.

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?

Three tight sentences with the staging constraint and update model front-loaded; the only waste is the unhelpful 'Tools revision' footer. Every sentence about behavior earns its place.

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 destructive mutation with an output schema and rich annotations, the description covers the crucial gaps: staging, non-destructive partial updates, and optimistic concurrency. It stops short of explaining the `container` scope or what the returned value represents, but an agent has enough to call it correctly.

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 compensate. It does partially: it defines `variable_id` (identifier) and explains the replacement semantics of `parameter` and `type` (whole list replaced when type changes). However, `container` and `name` receive no semantic clarification, leaving half the parameters unexplained in both schema and description.

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 ('Update a user-defined variable'), names the scope ('IN the managed AdCopilot workspace'), the identifier ('by variable id'), and the staging constraint ('staged, never published'). An agent can distinguish it from gtm_create_variable and gtm_list_variables without opening either 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?

Implies clear usage context: modify an existing variable by id, with partial-update semantics and conflict refusal. It does not name alternatives (e.g., gtm_create_variable for new variables) or explicitly state when not to use it, which keeps it just short of a 5.

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