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

Annotations already declare readOnlyHint and idempotentHint, yet the description adds genuinely new behavioral facts: it takes no arguments, works without signing in (auth behavior), costs nothing, and does not consume a check (quota side effect). It also documents null semantics for email and upgradeUrl and the usageUnavailable flag when today's count cannot be read.

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 purpose and the pre-call planning directive, and every sentence carries information. It is a single dense paragraph with parenthesized field and pricing detail, which is informative but slightly hard to scan; a short field list would read faster without losing content.

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?

There is no output schema, so the description must and does enumerate the return shape including null cases and the usageUnavailable edge case. Combined with auth, cost, and quota semantics for a zero-parameter tool, nothing an agent needs in order to call it correctly 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 the baseline is 4 and there is no parameter meaning to add. The description correctly signals this with 'Takes no arguments', sparing the agent from opening an empty schema.

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: 'Describes who SpotCheck thinks the caller is and what they can do right now.' The enumeration of returned fields (email, tier, isAnonymous, authMethod, features, allowance, upgradeUrl) makes it unmistakable against siblings like check_playlist or list_monitors, which are named as downstream consumers.

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?

Explicitly instructs 'Use it before other calls to plan' and then spells out the decision it enables for each sibling: whether check_playlist has checks left (with per-tier quotas), whether get_curator_contacts and the monitor tools will work (Premium), and whether the full factor breakdown is unlocked (Pro/Premium). This is concrete when-to-use routing with tier conditions, not vague advice.

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