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

Annotations only cover the coarse safety profile (readOnlyHint, openWorldHint, non-idempotent), while the description supplies the genuinely load-bearing behavior: an anonymous per-session trial identity is the default, this call returns a short-lived URL the user must open and approve, subsequent calls act as the real account, and clients that open a new MCP session each turn must re-link. The reference to the `acting_as` line also tells the agent how to verify which identity was used.

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?

Front-loaded with the purpose and trigger conditions, then the mechanics, then the user-facing action. The middle paragraph is dense but every sentence carries distinct information (default identity, return value, session binding, verification line); it is slightly long for a zero-argument tool but not 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?

An output schema exists so return structure needn't be spelled out, yet the description still names `link_url` and tells the agent what to do with it. Combined with the coverage of default identity and session semantics, nothing an agent needs to call and act on this tool is missing.

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?

The tool takes zero parameters, so there is nothing to disambiguate; the baseline for a parameterless schema is 4. The description correctly notes that 'Nothing else is required from them', reinforcing that the call is argument-free.

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 first sentence states a specific verb and resource ('Link this chat to the user's existing QuantifyMe account'), and the opening condition list distinguishes it from every sibling (none of which touch account identity). An agent can identify the tool's job from the title plus first line alone.

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 gives three explicit trigger conditions ('user says they already have an account', 'asks why their models are missing / where a model went', 'wants what they deploy here to show up in their dashboard'), which is precisely the when-to-use guidance an agent needs. It also names the default no-link path, implicitly defining when NOT to call it.

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