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

Annotations provide limited safety context (readOnlyHint=false, destructiveHint=false). The description adds the useful behavioral detail that compression can be lossy or lossless. However, it does not disclose the irreversibility of lossy re-encoding, default EXIF stripping, or output format implications beyond what the schema already states.

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 short and front-loaded with the tool's purpose. The '[category: photo]' suffix adds minor noise, and 'target-size mode' is vague, but overall the description is efficient and easy to parse.

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?

Given the tool has four parameters, no output schema, and basic annotations, the description provides a reasonable starting point but is incomplete. It lacks usage differentiation from photo_compress_to_size, does not explain the mysterious 'target-size mode,' and does not mention supported input formats (though schema covers this).

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 100%, so the schema fully documents all four parameters. The description adds minimal parameter-related meaning beyond mentioning 'JPEG quality setting' and 'target-size mode.' Notably, 'target-size mode' does not map to any schema parameter, which introduces ambiguity rather than clarifying semantics.

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 uses a specific verb and resource: 'Reduce image file size using lossy or lossless compression.' It clearly conveys the tool's core function. However, it does not explicitly distinguish itself from the closely related sibling photo_compress_to_size, even though it mentions 'target-size mode.'

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?

No guidance is given about when to use this tool versus alternatives. The sibling list includes photo_compress_to_size, which appears to overlap directly with the 'target-size mode' mentioned in the description, but the description does not clarify the difference or provide selection criteria.

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