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

Annotations already declare readOnlyHint=true, openWorldHint=true and destructiveHint=false, so the safety profile is covered. The description adds real context beyond that: the visibility scope is limited to what the account can see, and the output is a container identifier meant to be fed to sibling gtm_ tools. It stops short of mentioning result limits or pagination, so it is not fully complete.

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 compact sentences with no filler. The enumeration of returned fields comes first, followed by the actionable instruction, so the most decision-relevant content is front-loaded.

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?

With no output schema, the description does the work of describing the return shape and the follow-up usage, which is enough for an agent to call this correctly. Minor gap: nothing about whether the list can be truncated or how many containers are typically returned.

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?

The tool takes zero parameters, so the baseline is 4. The description instead documents the returned fields (public id like GTM-XXXX, name, web or server, domains), which is useful since there is no output schema, though it is technically return-value rather than parameter 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 ('List the Google Tag Manager containers') and narrows scope with 'this account can see', which separates it from gtm_container_overview and gtm_audit_container. It also names the returned fields, so an agent knows exactly what it gets.

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 explicit conditional: 'only needed when there's more than one', plus the downstream routing rule 'Pass one as `container` to the other gtm_ tools'. That tells the agent both when to call it and what to do with the result, which is exactly the guidance a zero-param discovery tool needs.

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