GTM: Accounts & containers

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

Annotations already declare readOnlyHint and openWorldHint, so the safety profile is covered. The description adds useful behavior beyond that by sketching the shape of the result set – publicId naming convention, numeric containerId, and container type web/server – which matters because there is no output 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?

Two sentences, front-loaded with the purpose and followed by the downstream dependency. Every clause – return fields, ID formats, the gtm_export_container link – carries information an agent would otherwise have to discover.

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 parameters and no output schema, the description supplies the essential missing piece: what each returned container looks like and how to use its IDs. It does not mention pagination, authentication scope, or whether all containers across all accounts are always fetched, which would round it out.

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; there is nothing for the description to clarify beyond noting that every account and container is returned without filtering, which the word 'all' does.

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 ('Lists all Google Tag Manager accounts and their containers') and names the concrete fields returned (publicId GTM-XXXX, numeric containerId, web/server). This distinguishes it from the single-item sibling gtm_lookup_container and from gtm_export_container, which consumes its output.

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?

The second sentence gives a clear usage context: it is the discovery step whose accountId + containerId feed gtm_export_container. It does not explicitly say when to prefer gtm_lookup_container or gtm_list_workspaces, so alternatives are implied rather than spelled out.

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