Write a caption

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

Annotations declare readOnlyHint=false, openWorldHint=true, and destructiveHint=false, so the safety profile is already covered. The description adds genuinely new behavior: a quota cost ('Costs a small amount of the account's text allowance'), a specific failure mode (409 with remediation 'set a website first'), and an information asymmetry the agent cannot otherwise detect.

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?

Four short sentences, front-loaded with purpose, then cost, then the blocking precondition, then the comparative rationale. No sentence is redundant and none repeats the schema 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?

With no output schema, the description should carry the return shape; it implies a caption plus hashtags are produced but does not say whether the copy is persisted to a post or returned for the agent to use, and does not cover idempotency. Prerequisites, cost, and failure mode are all covered, so the gap is modest.

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%, so the schema already documents all six parameters including the kind enum and the slideshow 'slides' array. The description adds no parameter-level detail (e.g., how 'scene' or 'overlay' influence the output), so the baseline 3 applies.

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 gives a specific verb and resource: 'Write a caption and hashtags in the workspace's brand voice for a piece of content,' which is more precise than the title 'Write a caption' (it also produces hashtags). No sibling tool writes captions, so differentiation is effectively automatic, but the description never names or contrasts a sibling, keeping this at a 4 rather than a 5.

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?

It states an explicit preference rule ('Prefer this over writing captions yourself'), the reason for it (it reads the brand voice, which you cannot see in full), and a hard precondition ('Requires a brand on the workspace — without one it fails with a 409'). An agent knows both when to reach for this tool and when it will fail.

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