Download a picked photo or video

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

Beyond the annotations (readOnlyHint, idempotentHint, etc.), the description discloses important behaviors: the underlying URL is transient and auth-scoped, large files are refused, and the default size suffix is capped. These details help an agent anticipate failures and choose parameters correctly, going well beyond what annotations alone 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?

The description is compact and front-loaded: the first sentence states the core function, the second gives the required input, and the following sentences provide only decision-relevant caveats. Every sentence earns its place, with no repetition of schema content or annotations.

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?

Although there is no output schema, the description specifies the return shape (base64 with mime type) and covers the critical operational constraints (auth, expiry, size caps, max_mb intent). The 4 parameters are fully documented in the schema, so nothing an agent needs to invoke correctly 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?

With 100% schema coverage, the baseline is 3, and the description adds extra meaning: it labels base_url as coming from list_picked_media and explains when to raise max_mb ('only when the caller genuinely needs the original'). The size and account parameters are well documented in the schema, and the description enriches the two most context-sensitive parameters.

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 clearly states the action ('Fetch the bytes') and the resource ('an item the user picked'), and specifies the return format (base64 with mime type). It also ties the input to list_picked_media, which scopes the tool distinctly from library download tools. However, it does not explicitly name or contrast the sibling download_media_item, so sibling differentiation is achieved only implicitly through the 'picked' vocabulary.

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 gives explicit when-to-use guidance: 'Use this rather than giving a base_url to the user or to another tool,' with the concrete reasons (auth header, size suffix, expiry within the hour). It also advises on max_mb, telling the agent to raise it only when the caller genuinely needs the original. This is strong, actionable routing guidance.

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