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

Annotations already declare readOnly/idempotent/open-world/non-destructive, so the safety profile is covered. The description adds genuinely non-structured context: the call is metered at $0.004 USDC on Base or Solana, requires an X-PAYMENT header, and offers a free trial via X-Trial: 1. What it does not cover is failure behavior when payment is missing or the trial is exhausted.

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 compact clauses with the output shape front-loaded and the payment terms second — nothing is padded. The payment clause is dense with header names, but each detail is operationally necessary for a paid call.

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?

Annotations and the inline return-field list mean an agent knows what comes back and that the call is safe, and no output schema is needed. However, with four undocumented parameters at 0% coverage and no note on payment failure or the q-vs-query split, the definition leaves an agent guessing at invocation details.

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% across four parameters, so the description must carry the burden and largely doesn't. 'One query' hints at q/query but never resolves why both exist or which is authoritative, gl (presumably country/locale) is never mentioned, and num is only indirectly implied by 'up to 20'.

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 exact resource and payload ('Image results (title, page url, imageUrl, thumbnail, size) for one query, up to 20'), which lets an agent separate it from web_search, video_search, and news_search without opening the schema. It stops short of an explicit sibling comparison, but the verb+resource+returned-field shape is unambiguous.

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?

Usage is only implied: an agent infers this is the tool for image results when it needs images rather than web pages or videos. There is no explicit 'use this instead of X when Y' routing, and no guidance on when to burn a paid call versus the free trial (X-Trial: 1) — a real decision point for a metered tool.

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