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

Annotations already declare readOnlyHint=false and destructiveHint=false; the description goes further by framing the operation as a 'copy' (original not mutated) and explaining the downstream effect that the returned media_id replaces the original in media_ids for create_post/update_post. It stops short of stating whether the original asset is retained or how the edge colour is chosen.

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?

Every sentence carries information (dimensions, rationale, when-not rule, return contract), but the opening is a dense run-on fragment with parenthetical piled on parenthetical rather than cleanly front-loaded statements.

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, yet the description still briefly states the return contract (new media_id and url) and its ripple effect on media_ids, closing the loop for an agent chaining this into create_post/update_post. Nothing needed to call it 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?

Only one parameter with 100% schema description coverage, so the schema already carries the semantics ('The slide (an image media_id)'). The description adds the useful constraint that the input is an image slide needing fit, but no format or naming detail beyond that. Baseline 3 applies.

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 (fit) and resource (slide) and defines the transformation concretely: 1080x1920, scaled to sit below TikTok's top 14%, centred, on its own edge colour. It is unmistakable against siblings like make_cover or suggest_cover.

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?

Gives explicit when-to-use conditions keyed to a sibling's output ('fixes what check_post reports as a slide's text under the tabs, or a slide that is not 9:16') and an explicit when-NOT: text between 14% and 65% of height needs no fitting.

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