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

Beyond the readOnlyHint/openWorldHint annotations, the description discloses sorting behavior, the 404 failure mode for unknown symbols, data version (v8), and a full pricing model ($0.002 per successful call via x402 on Base/Solana/Arc, failed calls not charged). This is exactly the context an agent needs before invoking a paid, open-world call.

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 dense sentences with the core behavior front-loaded and pricing/payment trailing. Every clause carries substantive information; no filler, though the payment details run long in a single clause.

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 an output schema present and readOnly/openWorld annotations covering the safety profile, the description fills the remaining gaps: payment model, error behavior, data version, and sort order. Nothing essential to invoking it correctly 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 coverage is 100%, so both parameters are documented at the schema level. The description reinforces the singular-gene scope and the GENCODE matching behavior, but adds no detail about the limit parameter beyond what the schema already provides.

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 and resource ('GTEx Portal gene expression'), plus exact scope: median TPM of one gene in human tissues, sorted highest first, with matched GENCODE id. It is unmistakable against the sibling set, which is dominated by news/article searches and security lookups.

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 useful calling context (public API v2, no key, GTEx v8, unknown symbols 404), which tells the agent what inputs succeed. However, there is no explicit 'use this when…' framing or exclusion guidance versus alternatives; usage is inferred from the self-evident gene-expression purpose rather than stated.

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