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

Beyond the readOnlyHint/openWorldHint annotations, the description discloses two non-obvious behaviors: the fixed 500-item scan window and the meaning of truncated=true. This is exactly the kind of caveat an agent needs to know before relying on the result — it cannot infer the scan limit or the partial-result flag from the schema and would otherwise assume the result is exhaustive.

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 with zero fluff: it front-loads the matching behavior, gives the platform rationale, and closes with the critical truncation caveat. Every sentence earns its place and the ordering is maximally informative.

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 and readOnlyHint/openWorldHint annotations covering the safety profile, most of the burden is already borne by structured fields. The description covers the key additional semantics (scan window, truncation). Minor gaps that remain are being explicit about result ordering and behavior on invalid playlist IDs, which are small for a 3-parameter search tool.

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 100% (id, q, limit each have meaningful descriptions with ranges and defaults), so the baseline is 3. The description adds only the case-insensitivity nuance about q via prose; no per-parameter detail is added beyond what the schema already provides.

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?

The first sentence states a specific verb+resource and the match mechanics: 'Find videos inside a playlist by a substring of the title (case-insensitive).' This clearly differentiates from siblings like search_youtube (global search), list_playlist_videos (full listing), and search_channel_videos (channel-scoped) by confining the search to an existing playlist.

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?

The rationale ('YouTube has no native playlist search, so this scans up to 500 playlist items') explains why the tool exists and tells the agent it is the workaround for that platform gap. However, it does not name any alternative tool, give explicit when-not-to-use guidance, or point to a sibling like list_playlist_videos for full enumeration, so the agent is left to infer the decision boundary.

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