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

With no annotations, the description carries the load. It discloses pricing ('Flat 1 credit'), billing safety ('Empty results and failures are never charged'), and cache behavior ('free 24h cache hit'). It could add error/auth details, but the key run-cost and failure-cost behaviors are well covered.

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?

The core scope is front-loaded and every clause earns its place, but 'Flat 1 credit. Costs 1 credit.' is a redundant repetition that could be collapsed into one phrase.

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?

Given only two simple parameters, a fully-covered schema, and no output schema, the description supplies what is missing: return fields, the crucial exclusion of videos, cost, failure-charge policy, and cache behavior. An agent has enough 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 coverage is 100%, so the schema already defines url and cache. The description's cache sentence adds practical context but mostly restates what the cache parameter description says ('24h response cache (0 credits on hit)', 'Default false'). No meaningful new parameter meaning beyond the schema.

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?

Description opens with a precise scope: 'Playlist metadata only' and enumerates exact fields (title, channel{}, totalVideos, thumbnailUrl). The explicit 'No videos[]' draws a clear line against the sibling youtube_playlist_videos, so an agent can select it without opening schemas.

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 clearly communicates when to use this tool: when only playlist metadata is needed, and 'No videos[]' rules out use when videos are required. It also gives a direct cache usage instruction. However, it never names the alternative youtube_playlist_videos explicitly, so the exclusion is implied rather than stated.

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