Charts: platform metrics

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

Annotations already cover the safety profile (readOnlyHint=true, openWorldHint=false), and the description adds useful context beyond them: it discloses the shape of each returned record and that the response is JSON. With no output schema present, describing return contents is genuinely valuable, though pagination/error behavior is not mentioned.

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 sentences, front-loaded with the core purpose and then the follow-up wiring. Slightly repetitive in restating 'usage metrics a platform chart can plot', but there is no filler and no buried information.

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 zero-parameter, side-effect-free lookup with no output schema, the description covers what the agent needs: what is listed, what each entry contains, and how to consume the ids downstream. Annotations already carry the read-only safety story, so the remaining gap is minor.

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 still adds meaning by explaining how the returned ids map onto parameters of other tools (platform_metric for charts_preview/charts_create, stack_by for breakdowns), which helps the agent use the output correctly.

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 (List) and resource (usage metrics a platform chart can plot), and enumerates exactly what each entry contains: id, label, shape, supported chart types and breakdowns. An agent can distinguish this discovery/lookup tool from siblings like charts_list, charts_get, charts_preview and charts_create without opening 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?

The description names the concrete alternatives and the workflow: 'Pass a metric's id as platform_metric to charts_preview or charts_create, and one of its breakdowns as stack_by.' That is strong context for when this tool is the right entry point. It stops short of an explicit when-not-to-use or ordering statement, so a 4 rather than a 5.

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