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

Annotations cover the safety profile (readOnly, idempotent, non-destructive), and the description adds substantial context beyond that: API key requirement, no job listing, in-call blocking up to 50s with progress notifications, and partial-failure behavior (failed variants don't suppress the rest). Behavioral traits beyond annotations are well disclosed.

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?

Front-loads the core purpose, then constraints, then parameter behavior, then return shape. Every sentence earns its place with no repetition of the name or title.

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?

With an output schema present, the description needn't document return fields, yet it helpfully summarizes status, stage, progress_percent and variants. Combined with prerequisite, auth, and partial-failure notes, an agent has everything needed to call it correctly.

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 already 100%, but the description reinforces wait_sec's semantics (default 30, max 50, 0 = snapshot, progress notifications) and explains why thumbnail_job_id matters (jobs can't be listed). This adds meaning beyond the schema despite the schema already being complete.

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 status and images of a thumbnail job) and explicitly ties it to its sibling create_youtube_thumbnails, making the pair unambiguous. An agent can immediately distinguish it from the create sibling and other get_* tools.

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?

Explicitly names the required prerequisite (keep thumbnail_job_id from create_youtube_thumbnails), notes jobs cannot be listed, and explains the wait_sec tradeoff (0 = snapshot vs default wait). This is a clear when/how-to-use contract with no inference required.

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