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

With no annotations, the description carries the full burden and does a good job: it discloses flat cost (1 credit), asynchronous execution with a pollable job_id, and a 1-hour expiry on result links. It stops short of failure behavior (invalid URLs, mismatched frame sizes) or rate limits, so not quite full marks.

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?

Three short sentences, front-loaded with what the tool produces, then cost, then async/expiry mechanics. Every sentence carries operational information an agent needs; nothing is padding.

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 stateless computation with no annotations and no output schema, the description covers the essentials: inputs (frames/icons), output shape (PNG + coordinate JSON), cost, async pattern, and link lifetime. The remaining hole is parameter-level detail, which is scored separately.

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 coverage is only 40%: 'images' and 'nearest' are documented in the schema, while 'columns', 'cell_width', and 'cell_height' are described nowhere. The phrase 'fixed cell size' gestures at the two cell dimensions but gives no defaults, ranges, or grid semantics, and 'columns' is never mentioned — so the description does not compensate for the coverage gap.

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+resource ('combine animation frames or icons into one sprite sheet PNG') and names both outputs (PNG sheet plus JSON frame coordinates), which cleanly separates it from neighbors like make_thumbnails or pixel_art. An agent can identify the tool's job without opening the schema.

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 concrete follow-up guidance ('Long jobs return a job_id; poll it with get_job'), which is a real workflow instruction. It does not, however, say when to prefer this over adjacent tools such as make_thumbnails or pixel_art, so selection guidance is only implied by the game-engine use case.

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