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

Goes well beyond the readOnly/idempotent annotations: it discloses latency (~1/3 second at 1024px), the byte/context cost ('previews are most of the bytes a session returns'), the proxy-vs-exact tradeoff, and that out-of-bounds regions are refused rather than clamped. These are exactly the traits an agent needs to budget calls.

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?

Four tight sentences, front-loaded with the core action, then cost, then routing, then the region nuance. No sentence is filler; the latency and byte-cost details are load-bearing for call budgeting.

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 the return type needn't be described further, and the description still covers performance, cost, exactness, and refusal behavior. Nothing an agent needs to call this 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 already 100%, so baseline is 3, but the description adds real meaning: region produces an exact full-resolution crop rather than the approximate whole-image proxy, and the 1024px latency figure gives max_px practical weight. It does not restate the coordinate syntax, which the schema already covers.

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?

States a specific verb and resource — render the filtered photo as a JPEG — and explicitly frames it as the visual counterpart to get_histogram. An agent can distinguish it from numeric/sibling inspection tools without opening any 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?

Explicitly routes between alternatives: prefer get_histogram for a numeric check, use this for spatial questions, and use region when an exact full-resolution crop is needed. It names both the alternative and the condition that selects it.

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