Read a market session

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 safety profile is covered. The description adds genuine value on top: the visibility boundary ('shows what a trader could see and nothing of the simulator's own state') and the fact it runs no market, which is not captured by the annotations.

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 the core action and scope, then the optional ticker behavior, then the session_id branch. The enumeration is dense but every clause conveys distinct content the agent needs, with no filler.

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?

An output schema exists, so return values need no explanation, yet the description still orients the agent on what the response contains. Combined with full schema coverage and strong annotation coverage, nothing needed to call this tool 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?

Schema description coverage is 100%, so both parameters are already documented. The description restates the tickers detail fields and the omit-session_id behavior rather than adding syntax, format, or edge-case guidance beyond the schema, so baseline 3 is appropriate.

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 ('Read an open session without changing it') and enumerates exactly what the read returns: clock, prices, macro figures, news, portfolios, open orders, rewind checkpoints. It also implicitly distinguishes itself from session_step ('Runs no market') and references session_rewind, so an agent can place it among its siblings 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?

Gives clear operating context: read-only, no market advance, and the key branch 'Omit session_id to list the open sessions.' It does not explicitly name the alternative to reach for when you want to mutate state (e.g. session_step/session_fork), but the constraints make the intended use unambiguous.

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