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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, openWorld), yet the description adds substantial non-obvious behavior: two parallel upstream requests, a ~5-minute ETag cache on /v1/me, and that force_refresh adds Cache-Control: no-cache. It also documents the failure mode (MCPError when the key is invalid). This is meaningfully more than the annotations convey.

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?

The purpose is front-loaded as the first sentence, followed by mechanism, returns, and error. The Returns/Raises blocks are long but earn their place because no output schema exists. Slightly verbose for a one-parameter read tool.

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 correctly supplies the return shape (accounts, models, quota) and the error case, plus caching semantics for the sole parameter. The main omission is routing guidance versus the several sibling listing tools, which is minor for a read-only discovery call.

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 coverage is 0% for the single force_refresh parameter, so the description carries the full burden and does so well: it explains the ETag cache window and exactly what force_refresh=True changes. An agent can set the parameter correctly without reading any schema text.

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 opening line states a specific resource and outcome in plain terms: which LLM models this key can use right now and the key's quota. It also names the two upstream endpoints it aggregates (GET /llm/models and GET /v1/me), making the scope concrete. It stops short of distinguishing itself from near-siblings such as list_models, list_live_models, or refresh_llm_models, so the agent must infer the boundary.

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?

Usage context is implied (call it to discover available models and quota) and the caching/refresh behavior is explained, but there is no explicit 'use this instead of X when Y' routing against list_models, list_live_models, or check_credits. No prerequisites or exclusions are stated.

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