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

Annotations already declare readOnlyHint=true, openWorldHint=true and destructiveHint=false, so safety is covered. The description adds genuinely non-structured behavior: failed/unreadable profiles are not billed, and payment must be on Base or Polygon (not Solana). That billing and chain-availability context is exactly the kind of information annotations cannot 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?

Three sentences, front-loaded with the core action and return payload, followed by usage and then the payment/chain caveat. Dense and nearly waste-free, though the Solana/Base/Polygon clause sits awkwardly in a lookup description and the usage clause adds little.

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 appropriately enumerates the returned JSON fields so the agent knows what it gets. Billing behavior and chain availability are covered. The only missing element is how it differs from the generic "instagram" sibling, which matters given the crowded Instagram tool family.

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 100% and the single parameter already documents "Instagram username, without @; one public account per call." The description's "by username" and "one public account" simply restate that, adding no new format or edge-case guidance. Baseline 3 applies when the schema carries parameter meaning.

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 opens with a specific verb and resource: "Look up one public Instagram account by username," and enumerates the returned fields (biography, website, follower/following counts, post count, business category, verification). This separates it from the comments/reels-oriented Instagram siblings, though it never explicitly distinguishes it from the bare "instagram" sibling, which an agent could reasonably confuse with a profile lookup.

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?

"Use it for account research and creator comparisons" gives an implied usage context, and the payment-network note sets an eligibility constraint. However, there is no statement of when NOT to use it or which sibling (e.g. instagram, instagram-comments) to pick instead — the alternative to this tool is left for the agent to infer from the name alone.

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