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

Annotations already declare readOnlyHint=true and openWorldHint=true, so the safety profile is covered. The description adds real value beyond that: the validation failure mode ('account_id ist rein numerisch, sonst {"error":"invalid_id"}') and the workspace optionality rule, letting the agent avoid a predictable error.

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 short lines, front-loaded with the resource and prerequisite, with no filler. The embedded error-string literal is slightly noisy but earns its place by preventing a failure.

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 two-parameter read-only list tool with an output schema, the description covers the prerequisite chain, the validation constraint, and the one optional parameter's semantics. Nothing essential to a correct call is missing.

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, and it does: account_id is documented as purely numeric with its source tool, and workspace as the customer workspace slug that is optional when only one exists. It still does not clarify case/slug format edge cases for workspace.

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 states the resource and scope: containers belonging to a GTM account, keyed by account_id. The list verb is carried by the name/title rather than the description body, and it does not distinguish itself from siblings like gtm_container_info, but an agent can identify the operation.

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 gives concrete prerequisite routing ('account_id aus gtm_list_accounts') and states the condition under which workspace may be omitted ('optional bei nur einem Workspace'). It stops short of naming alternatives such as gtm_container_info vs. gtm_list_workspaces, so no explicit exclusion rules.

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