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

Annotations already declare readOnlyHint and openWorldHint=false, but the description adds non-obvious behavior: links are signed, they expire, and results should not be cached. That expiry/re-fetch contract is exactly the kind of context annotations cannot convey.

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?

One sentence, front-loaded with the return value, with the expiry caveat parenthetically attached. No wasted words.

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?

No output schema exists, and the description names what comes back (MP4 + thumbnail links), which covers the main gap. Minor omissions like behavior for exercises with no media or error/auth conditions keep it from a 5.

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 100% and the single id parameter is documented in-schema with a format example. The description only says 'one exercise' without adding ID format or id-resolution details, so the schema does the heavy lifting – baseline 3.

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: returns signed MP4 and thumbnail links for one exercise. It's clearly distinct from get_exercise (metadata) by naming the exact artifacts returned, though it doesn't name any sibling explicitly.

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 clear usage context: use it to get fresh links, and the parenthetical instructs the agent not to store them but to call again. It lacks an explicit 'use get_exercise for metadata instead' routing, which keeps it from a 5.

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