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

Annotations already declare readOnlyHint=true and openWorldHint=false, and the description adds useful context beyond them: the catalog is identical for every caller and workspace only fills the request path, plus it explains the 'companions' semantics of the response. No rate-limit, auth, or size caveats, but the added behavioral detail is meaningful.

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?

Front-loaded with purpose, followed by usage, parameter docs, and a worked example; each block earns its place. The lead sentence is dense and the companions parenthetical lengthens it, but there is no genuinely wasted text.

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 three-param, zero-required discovery tool with an output schema and read-only annotations, the description covers purpose, all parameters with valid values, behavioral nuance, and a concrete invocation example. Nothing essential to calling it correctly 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 carries the full burden and does so completely: workspace (name/id, content-invariant), group (filter with concrete examples like cost/latency/ttft), and kind (filter with its three valid values scalar/series/breakdown). This compensates fully for the undocumented schema.

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?

Opens with a specific verb+resource ('List every metric the platform knows how to compute') and enumerates the returned facts (unit, nullability, serving read, companions), making the tool's scope unambiguous. It does not explicitly contrast itself with nearby siblings such as workspace_metrics_overview or the other catalog tools, so it falls just short of 5.

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?

States a clear use case: 'Use it to discover exact field names instead of guessing them,' which tells the agent this is a discovery/introspection tool. It never names an alternative or a when-not-to-use condition (e.g., use workspace_metrics_overview for actual values), so there are no explicit exclusions.

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