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

Annotations already declare readOnly/idempotent/non-destructive, and the description goes well beyond them: ~900s response caching, X-Api-Key or x402 proof auth, HTTP 402 behavior for anonymous callers, $0.001 USDC per call with free linked keys, and a 60/min rate limit. This is exactly the operational context an agent cannot infer from structured fields.

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?

The leading sentence and the "Purpose:" line state the identical coverage list verbatim, which is pure duplication and dilutes the front-loading. The remaining auth/cost/rate-limit lines each earn their place, so the flaw is redundancy rather than bloat.

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 an output schema present, return values need no elaboration, and the description still sketches the multi-category payload. Auth, cost, caching, rate limit and research-only intent are all covered, leaving nothing an agent needs before calling.

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?

There is only one parameter and schema coverage is 100%, so the baseline is already met; the description adds the meaning the schema implies by tying __x_payment to the X-PAYMENT header and the retry-after-402 workflow. It correctly frames it as a non-business parameter.

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 resource with exhaustive scope: stock indices, metals, energy, tokenized equity perpetuals, forex, DXY (ECB reference rates) and Treasury yields. That enumeration distinguishes it cleanly from siblings like cc.funding_rates, cc.etf_flows or cc.cme_gap without opening a schema.

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?

"Use for research / signal context" plus "Pair with cc.agent_strategy (paper) before any live order" and "Do not invent fills from this data alone" give concrete usage and a named companion tool. No explicit when-not-to-use or alternative-quote-source routing, so it falls short of a 5.

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