Custom playlist cover image

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

Annotations (readOnlyHint:false, destructiveHint:false) already indicate mutation, but the description adds critical behavioral details: the HTTP 500 'Internal error encountered' masking real errors, the imageUrl must be Hermoso-hosted (nothing else fetched server-side), and the need for a verified YouTube channel. These are beyond annotations and significantly aid an agent in anticipating and diagnosing failures. No contradiction with annotations.

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 description is dense but well-structured, opening with the core purpose and then detailing constraints, actions, and error behavior. Each sentence carries relevant information; the HTTP 500 explanation is a bit verbose but important for agent behavior. It is not as succinct as the gold standard but remains efficient given the tool's complexity.

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 tool with four parameters, an enum, and a multi-step chain, the description covers all crucial aspects: purpose, action semantics, URL constraints, error handling (including the misleading HTTP 500 and its resolution path via verification), and the relationship to sibling tools. No output schema exists, but the description does not need to explain return values. Nothing essential is missing.

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 covers 100% of parameters, each with a short description. The description adds meaningful context: action defaults to 'list', imageUrl must be a Hermoso-hosted URL up to 50MB and must come from make_thumbnail, a Hermoso render, or upload_file; imageId for delete comes from action:'list'. This goes beyond the schema's terse hints, making the constraints actionable.

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 description opens with 'PUT A CUSTOM COVER ON A PLAYLIST' — a specific verb and resource. It clearly explains the three actions (list, set, delete) and distinguishes itself from siblings by noting that make_thumbnail renders artwork and playlist tools own the playlist. This is unambiguous and differentiates it from related tools like set_youtube_thumbnail.

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 description explains the chain context (last call after make_thumbnail or upload_file), states what each action does, and gives explicit requirements for imageUrl (Hermoso-hosted, ≤50MB). It also mentions the channel verification prerequisite and contrasts with the sibling set_youtube_thumbnail on unverified channels. It does not explicitly say 'use this instead of X' but the context is clear. A minor gap is the lack of guidance on when to choose 'list' vs 'set' beyond their descriptions.

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