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

Annotations already declare a non-read-only, non-destructive mutation, but the description adds real value beyond them by disclosing the two-phase safety model: confirm=false previews and confirm=true actually creates. This preview semantics is not derivable from the annotations or schema, and the mention of a generated 'GTM-XXXX' id hints that repeated calls produce distinct resources.

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-loads the purpose before parameters and safety, and every clause carries information. The dense em-dash formatting is slightly cluttered but not wasteful; a separate line for SAFETY would improve scannability.

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 3-parameter mutation tool with an output schema (so return values needn't be described), the definition covers purpose, the account prerequisite, and the confirm safeguard. Only the 'name' parameter lacks explicit documentation, which is a minor gap.

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 burden. It fully explains 'account' (list_gtm_accounts value or name/id, empty if only one) and 'confirm' (preview vs create), covering the two non-obvious parameters; only 'name' is left to obvious inference as the container name.

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 ('Creates') and resource ('web CONTAINER in a GTM account') and clarifies what a container is (isolated space with its own tags/triggers/variables and a 'GTM-XXXX' id). This clearly distinguishes it from create_gtm_tag, create_gtm_trigger, create_gtm_variable, and create_gtm_workspace without needing to open any 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 an actionable prerequisite by directing the agent to list_gtm_accounts for the account value and explaining the empty-string fallback when only one account exists. It does not explicitly state when-not to use it (e.g., versus create_gtm_workspace), but the creation context is clear and well-scoped.

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