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

Annotations already declare readOnlyHint=true, openWorldHint=false and destructiveHint=false, so the safety profile is covered. The description adds value beyond the structured fields by disclosing an authentication prerequisite ('Needs a free StartupHub.ai account'), which is material behavioral context an agent would otherwise not know. It stops short of rate limits or pagination behavior, so not a 5.

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 with no filler; the returned-field inventory is front-loaded and the usage condition follows. The first sentence is dense to the point of being a run-on, but every clause carries information an agent needs.

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?

There is no output schema, and the description compensates by enumerating the return payload in detail, including the aggregate summary (total raised, latest round date/series). Combined with the annotation-covered safety profile and the stated account requirement, nothing essential for a correct call 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% for the single 'slug' parameter, so the description must carry the burden. It implies the identifier refers to a startup via 'for a startup' and the get_startup cross-reference, but never states the slug's format or where an agent obtains it. This partially compensates for the coverage gap, matching the baseline 3.

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 states a specific verb+resource ('Full chronological list of investment rounds for a startup') and enumerates the exact fields returned (amount, series, date, pre/post-money valuation, investor IDs, plus summary totals). It explicitly contrasts itself with get_startup and total_funding, so an agent can distinguish it from siblings without opening a schema.

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?

It gives a clear conditional trigger: 'Use after get_startup if you need round-by-round detail rather than just total_funding.' That is explicit when-to-use plus an alternative. It does not address the other funding-adjacent siblings such as query_funding or get_company_funding, so routing between those and this tool is left to inference.

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