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

Annotations already declare read-only/idempotent/non-destructive, and the description adds materially more: that it is free, that it works with no key, that keyless callers at one address share a quota, and the exact endpoint and header/query forms for obtaining a personal key. Error behavior ('none; it answers without a key too') is also disclosed.

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 usage before the field list. The parenthetical enumeration of returned fields is dense but each item earns its place given there is no output schema; slightly long, though 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?

With no output schema, the description carries the return-value burden and does so fully: named fields, their meanings, the tier/keyProblem states, and node status fields. Auth, quota-sharing semantics, cost model, and error behavior are all covered for a zero-parameter tool.

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?

Zero parameters, so the baseline is 4. The description reinforces this ('no parameters') and adds the non-schema auth detail that a key may be supplied via Authorization: Bearer or ?key= on the MCP URL, which is genuinely useful invocation context.

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: reads the caller's remaining spend plus the node's busy state. The scope is narrow and self-contained, and no sibling tool (arena_*, plan_*, market_*) overlaps with it, so an agent can route here unambiguously.

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?

Gives two concrete triggers: before a run of plans, or after a refusal to learn how long to wait. It does not name an alternative tool or a when-not condition, but no sibling covers this diagnostic role, so the gap is small.

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