img_compare

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

With no annotations, the description transparently explains the tool's behavior: it performs pixel-by-pixel comparison and reports quantitative results. It does not mention side effects or access requirements, but the tool is inherently read-only and non-destructive.

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?

The description is extremely concise, consisting of three sentences with no redundancies. Every sentence adds essential information: operation, output details, and use case.

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?

For a simple two-parameter tool with no output schema, the description is mostly complete, covering what it does and what it reports. However, it omits prerequisites like same image dimensions or format, which could affect usage.

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?

Both parameters have schema descriptions ('Path to first image file', 'Path to second image file') providing full coverage. The description adds context by tying parameters to the comparison operation but does not add new semantic details 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 clearly states the verb (pixel-by-pixel comparison) and resource (two images), and specifies the outputs (identical/different pixel counts, max difference, affected channels). It distinguishes from sibling tools like img_lsb_detect by focusing on general pixel-level comparison for steganography detection.

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?

The description indicates usefulness for detecting steganographic modifications, providing a use case. However, it does not explicitly guide when to use this tool over alternatives like img_lsb_detect or img_chi_square, nor does it state when not to use it.

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