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

Annotations cover read-only/idempotency/open-world, but the description adds genuinely new behavior: it overwrites the existing slot ('It replaces what that slot had') and defines the failure mode ('An id that matches nothing returns an error'). It also scopes the voiceover slot to the person's own sounds. The overwrite disclosure sits in mild tension with destructiveHint=false, though replacing an assignment (not deleting the underlying media) is arguably reversible and idempotent.

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?

Purpose is front-loaded, but the text is wordy and partly redundant ('by its id' recurs; 'already in LFG' appears twice) and the second sentence is a fragment that restates the first before pivoting to alternatives. It is readable but not tight.

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 3-parameter mutation tool with no output schema, the description covers purpose, sibling routing, slot semantics, overwrite behavior, and the error case. Only minor gaps remain (e.g., ownership/permission prerequisites beyond 'an alarm the person made').

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 baseline is 3, but the description adds a constraint not present in the schema: 'use' selects wallpaper/song/voiceover and voiceover is limited to the person's own sounds. It also clarifies that media_id can be a library sound id, a drawn look id, or an upload id.

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 and resource ('Puts something already in LFG on an alarm ... a library sound, a drawn look or theme picture, or one of the person's own uploads'), and enumerates the accepted media classes so the tool is distinguishable from set_gif and the add_media_* family. An agent can tell what it does without opening the schema.

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?

Gives explicit routing conditions: use this for something already in LFG with an id, whereas 'a new file goes on by link, as a file, or through the one-time page, and a KLIPY GIF by its address'. The alternatives are described functionally rather than named (add_media_file, add_media_from_url, set_gif), so the agent must map descriptions to sibling names itself.

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