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

readOnlyHint=true already covers the safety profile, so the description's job is lighter. It adds genuine context beyond the annotation: the return content (providers with per-provider model counts) and the provider/channel taxonomy that governs interpretation of the results. No pagination or rate-limit detail, but the conceptual framing is the valuable part here.

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 operation and payload before the taxonomy caveat. The parenthetical channel list (Vertex, Bedrock, Azure, OpenRouter) is slightly dense but earns its place by making the counter-example concrete.

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 must convey the return shape, and it does ('how many models each has'). For a zero-parameter read tool with readOnlyHint set, that is sufficient to call and interpret it correctly; only pagination/ordering behaviour is left unstated.

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, which is the baseline-4 case. The description adds nothing parameter-related because there is nothing to add; it correctly focuses on the conceptual distinction instead.

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 every provider in the catalogue') plus the payload ('how many models each has'), so the agent knows exactly what it gets. It also pre-empts the most likely confusion by defining what counts as a provider versus a sales channel, which is the differentiation that matters most among these siblings.

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?

Explicitly routes the agent away from this tool when it actually wants channel pricing, naming the alternative (`get_model_price` with a `channel`) and the condition that selects it. It does not address other plausible neighbours such as search_models or compare_models, so guidance is clear but not exhaustive.

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