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

Annotations establish the safe read-only, idempotent profile. The description adds genuinely new context: the URL is signed, requires the recordings:read scope, and expires. That scope requirement in particular is not derivable from annotations or schema. It doesn't state the URL's eventual failure mode when expired, keeping it at 4.

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, front-loaded with the core action and asset type, no padding. 'Same expiry semantics' is a dangling reference that assumes the reader has just seen a sibling definition, a minor structural flaw.

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 no output schema, the description does state the return value (a signed URL) and its auth scope, and all four parameters are schema-documented. An agent could call this correctly; only the expiry default and the expected error on an expired URL are left implicit.

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 recordingId, account, workspace and expiryMinutes are already documented in structured form. The phrase 'Same expiry semantics' gestures at expiryMinutes but adds no detail beyond the schema's 'Default 30', so baseline 3 is correct.

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 ('Get a signed URL for the recording's preview thumbnail') and immediately clarifies what the asset is (still image or short looping clip). It implicitly differentiates from hub_get_audio_url and hub_get_media_url by naming the preview thumbnail, though it never names those siblings explicitly.

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?

'Useful for embedding a card' gives one positive use case, which is more than nothing. But there is no explicit routing guidance to hub_get_media_url or hub_get_audio_url, and no statement of when this tool is not appropriate.

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