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

Annotations already cover safety (readOnlyHint=false, idempotentHint=true, destructiveHint=false), so the bar is lower, yet the description still adds real behavior: patch semantics ('what is not given stays') and the explicit boundary that membership is untouched. It omits permission requirements and any failure behavior for an unknown circle or slug collision.

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?

Very short and reasonably front-loaded, with the scope constraint first and the membership exclusion last. But the terseness crosses into under-specification: the opening is a sentence fragment and 'line' reads like a truncated internal label rather than a field name an agent can act on.

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 six-parameter mutation tool with no output schema, the definition covers patch semantics and non-goals but not permissions, identifier resolution, or what happens on conflicting slugs. Combined with the unexplained 'line', the agent has enough to attempt the call but not enough to call it confidently.

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 50%, and the description compensates only partly: it names name, slug and the join page, and its partial-update clause explains why optional fields may be omitted. It leaves 'line' ambiguous (presumably description), and never touches the required 'circle' identifier beyond what the schema already documents.

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 fragment 'A circle's name, slug, line or join page' plus the site scoping makes it clear this edits circle metadata, and 'Who is in it does not change' separates it from membership tools. However, the description never states an explicit verb (the action is only implied by the title 'Change a circle'), and 'line' is an unexplained term that an agent cannot map confidently to a field.

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?

Usage is only implied: 'what is not given stays' signals a partial update, and 'Who is in it does not change' routes membership changes to add_to_circle/remove_from_circle. It never names those siblings or states prerequisites such as needing an existing circle from list_circles, so the agent must infer the workflow.

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