SMX: market midpoint from the agent API (paid)

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

Annotations only cover read-only/open-world/idempotency hints; the description adds substantial behavioral context: exact payment amount and chain/asset, the env var that funds the charge, the consequence of missing it (no call), and the billing exception for 400/404. It also flags a field-format gotcha (legacy midCents is in basis points), which explains why the call is non-idempotent from a cost perspective.

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?

One dense, front-loaded paragraph: what it returns first, then the midCents unit warning, then payment/auth mechanics, then error billing. Every sentence carries information an agent needs and none is redundant.

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 enumerates the returned fields and their semantics (5000 = 50 cents) plus the payment prerequisite, so an agent can call and interpret results correctly. Nothing material is missing for a single-parameter read 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?

Schema description coverage is 100% and the single 'id' parameter is already documented with its source (smx_list_markets) and pattern. The description restates that it targets one market but adds no syntax or format detail beyond the schema, so baseline 3 applies.

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/resource (midpoint), names the exact endpoint (GET /v1/markets/{id}/mid), and scopes it to one SMX testnet market. The returned fields (midBps, midPriceCents, source, status) make the resource unambiguous, and the 'paid' framing separates it from the free sibling smx_get_market.

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?

Clear context: paid $0.01 call requiring X402_PRIVATE_KEY, and explicitly states no call is made without that key, plus errors 400/404 are not charged. It does not explicitly contrast itself with the free smx_get_market sibling, so the agent must infer when the paid path is warranted.

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