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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so the bar is lower, yet the description adds real behavioral context: one call auction per market per minute in US regular hours at the reference midpoint, and the notable limitation that only book size is exposed, never depth. It does not give any detail on how results are keyed or paginated, so it stops short of 5.

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?

All content is crammed into a single colon-led run-on sentence with a long comma-delimited field list. It is dense and information-rich with no filler, but it is not front-loaded and is hard to scan; splitting into a purpose sentence and a returns sentence would help.

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 carry the return-value burden, and it does enumerate the returned categories, including the pricing source and the hidden/visible distinction. For a zero-parameter read-only tool this is nearly complete; only the exact shape of session and market entries ('what is hidden and what is not') stays vague.

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 no parameters, so there is no parameter semantics to explain; the baseline of 4 applies. The description correctly implies the call needs no arguments to return the full venue and market overview.

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 description names a specific resource (Zero Dark, Borro's dark pool for stock tokens on Robinhood Chain) and enumerates the facts it returns: open state, sessions, next batch, reference price and its source, book size, lot size and caps, fee, and hidden vs visible data. An agent can tell this is the venue/market reference-data tool, though it does not explicitly differentiate itself from siblings such as markets, market, or darkroom_tape.

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?

Usage is only implied: by listing session state, batch timing, lot sizes and fees, it suggests calling this before placing an order via darkroom_order or registering a session. There is no explicit when-to-use statement, no exclusion of overlapping siblings like markets or darkroom_tape, and no stated prerequisites.

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