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

Beyond the annotations, the description discloses concrete safety behaviors: it rejects intranet addresses, path traversal, links/symlinks, and existing-file overwrites. These details meaningfully shape how an agent can expect the tool to behave.

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?

A single, well-structured sentence with no filler. The primary action is stated first, followed by a clear semicolon-separated list of rejection conditions.

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?

The description covers the core behavior, security constraints, and path semantics well, and an output schema exists to document return values. The only notable omission is behavior related to maxBytes, which is less critical because the parameter schema provides defaults and bounds.

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%, and the description partially compensates by clarifying that url must be a public HTTPS address and outputPath is a relative path. It does not explain maxBytes or what happens when the limit is exceeded, though the schema's default and maximum provide partial guidance.

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 a specific verb ('download') and resource ('image') and precisely defines the target location as a relative path under the current working directory. It also distances itself from siblings by focusing on fetching an existing image rather than generating or validating one.

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 clear context: use it only for HTTPS public addresses and relative output paths, and it lists rejected inputs such as intranet addresses and path traversal. It does not explicitly name sibling alternatives as choices, but the download-vs-generate/validate distinction is implicit.

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