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

Annotations already cover readOnly/idempotent/openWorld, and the description adds genuinely useful operational context beyond them: private addresses are refused (SSRF guard), input capped at 10 MB, and the result is returned as base64. It is consistent with readOnlyHint and does not contradict any annotation, though it says nothing about output format details or error behavior.

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?

Five short sentences, each carrying a distinct fact (mode, fit, input, limits, return), with the core purpose front-loaded and no filler. Well sized for the tool's complexity.

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?

An output schema exists so return values needn't be explained, and safety constraints are covered. However, for a 7-parameter tool with very low schema coverage, key semantics — aspect-ratio behavior, whether width/height/percent are mutually exclusive, defaults of lockAspect — are absent from both schema and description.

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 only 14%, so the description must carry the parameter burden, but it mostly repeats enum values already in the schema ('contain, cover, or stretch', 'pixels or percent'). It says nothing about width, height, lockAspect, or how percent interacts with them, leaving most of the 7 parameters unexplained.

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 states a specific verb and resource ('Resize an image') plus the two operating modes ('by pixels or percent'), so the agent knows exactly what transformation happens. It does not, however, distinguish this from close siblings such as crop_image, convert_image, or compress_image.

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 input guidance ('Send base64 or a public URL') which implies how the tool is invoked, and the size/address limits imply acceptable inputs. There is no explicit when-to-use versus the many image siblings (crop_image, compress_image, convert_image), so routing is left to inference.

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