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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so the safety profile is fully covered without description help. The description adds genuine context by enumerating what Pro unlocks (history since Jan 2024, same-day data, per-fund breakdown, CSV, higher rate limits), but it never says what the response actually looks like for an informational endpoint that has no output schema.

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?

A single front-loaded sentence with the actionable part ('how to get a free API key or upgrade to Pro') first and the detail list second. Nothing is wasted or repeated from structured fields.

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 no-parameter static info endpoint with full annotation coverage, the description covers subject matter adequately. The only gap is that, absent an output schema, it doesn't hint at the response form (text guidance, link, or structured plan data).

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 is nothing for the description to disambiguate; baseline 4 applies. The parenthetical feature list gives useful framing for what the returned guidance will cover.

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 concretely: instructions for obtaining a free API key or upgrading to Pro, plus what each tier includes. That is clearly distinguishable from the sibling flow-data tools, which return market data rather than onboarding/pricing information. It stops short of a crisp verb+resource framing but leaves no doubt about what the tool returns.

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?

There is no explicit 'use this when…' statement, but the nature of the tool (a static informational endpoint about API keys and Pro plans) makes the trigger self-evident, and no sibling overlaps with it, so the agent will not mis-route. No alternatives or exclusions are stated, keeping this at minimum-viable-plus.

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