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

Adds real behavior beyond the annotations: the credential's scope is limited to helper_* tools and /api/activity/relay*, it expires when the call ends, and rotate=true invalidates every earlier helper credential for this call. That rotate semantics is exactly the kind of side effect annotations (destructiveHint=false, idempotentHint=false) don't 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?

A single dense paragraph front-loads the return value and its audience, then layers label format, rotate semantics, and scope limits. Every clause carries information an agent needs; nothing is padded.

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?

Given an output schema exists, return values are covered, yet the description still adds the lifetime ('ends with the call') and the tool-scope restriction, which are critical to correct invocation. Complete enough that an agent could use the credential safely.

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 still enriches parameters: label is the helper's machine name (max 22 chars) rendered as 'Helper <label>: <helper_name>', and rotate's invalidation effect is spelled out beyond the schema's terse wording.

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+resource ('returns a helper credential token') and immediately enumerates the return payload (url, expires_in). It also distinguishes itself from siblings by describing the helper's role (add status/decisions/activity without joining, no voice, no chip) versus join/say.

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?

Clearly frames the use case ('other sessions working for the same person add their own status board... without joining') and the exclusions ('never for say or join'). It stops short of naming a competing sibling to pick instead, so the when-to-use-vs-alternative routing is implied rather than explicit.

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