List Tag Manager containers

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

Annotations already declare readOnlyHint, openWorldHint, idempotentHint, and destructiveHint=false, covering the safety profile. The description adds genuinely useful behavior beyond structured data: the response contains two distinct IDs, publicId versus containerId, and only the numeric containerId is usable by other GTM tools. This is important behavioral context not present in annotations or schema.

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 three sentences and front-loads the core action before the prerequisite and the high-value ID warning. The only waste is the final 'Read-only,' which merely restates the readOnlyHint annotation, so it does not quite earn a 5.

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 read-only list tool with no output schema, the description covers the two most important operational facts: the prerequisite accountId discovery and the ambiguity between containerId and publicId. Pagination and limit behavior are already documented in the schema, and the safety profile is covered by annotations. It is sufficient for correct invocation without needing full response-shape documentation.

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 the schema already documents accountId with/without prefix, limit defaulting, and pageToken. The description does not add new parameter-level semantics, only reinforcing the containerId warning that mostly matters for interpreting the response. Baseline 3 is appropriate because the schema carries the parameter documentation burden.

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 opens with 'Lists containers in a Tag Manager account,' a specific verb and resource with no ambiguity. The prerequisite mention of gtm_list_accounts and the focus on containerId clearly distinguish it from sibling list tools like gtm_list_workspaces or gtm_list_tags.

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?

It explicitly instructs the agent to call gtm_list_accounts first to obtain accountId, establishing the correct invocation sequence. It also warns to pass the numeric containerId rather than publicId, which is direct guidance for downstream use. It does not name explicit alternatives or state when not to use the tool, so it stops 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.