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

Annotations declare readOnlyHint and openWorldHint, and the description adds information they do not cover: no API key or authentication is required and the prices returned are live rather than cached. That is genuine added behavioral value, though it says nothing about rate limits, pagination, or result size.

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 short fragments, zero filler, and the core content ('plans and their live prices') is front-loaded before the access note. Nothing to trim.

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, read-only public listing with no output schema, the description covers what is returned and the auth posture, which is most of what an agent needs. It could still note response shape (currency, plan tiers) but the 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 there are no parameter semantics to explain; the baseline for a no-param tool is 4. The description correctly implies the call is unfiltered.

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 names the resource and its payload ('subscription plans and their live prices'), so an agent knows what comes back, but there is no verb and no scope statement. Sibling tools (backtest_*, coverage, check_strategy) don't overlap, so disambiguation pressure is low, yet the phrasing 'Data subscription plans' is slightly ambiguous as to whether it is a catalog listing or a plan-management surface.

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?

'Public, no key' tells the agent it can call this without credentials, which is useful invocation context, but it never says when to use this versus the sibling tools or in what workflow it belongs. Usage is only implied.

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