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

Annotations only declare the generic profile (not read-only, not idempotent, not destructive), so the description must add real behavior — and it does: call-once semantics, the hold-out being settable only at creation, and the single sibling that may later test it. It stops short of saying what happens on a duplicate call (error vs. new study), which is the one behavioral detail an agent would still want.

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?

Two dense clauses with zero filler: the purpose/definition comes first, then the ordering constraint, then the hold-out rule. Every phrase carries a distinct fact.

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, and both parameters are fully documented in the schema. Combined with the description's statement of lifecycle and ordering, an agent has everything needed to invoke this correctly.

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 coverage is 100%, so the baseline would be 3, but the description adds meaning the schema does not: hold_out is a period that every run is excluded from except run_held_out_test. That is a substantive semantic clarification of a nested object's role rather than a restatement of its fields.

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 ('Opens a study') and immediately defines the resource in domain terms ('the named set of runs every backtest belongs to'). It names the sibling tools it relates to (run_backtest, run_held_out_test), so an agent can place it in the workflow 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 explicit ordering and cardinality: 'call it once per question, before run_backtest.' It also states the unique condition for the hold-out option ('once and only here') plus the exception that consumes it (run_held_out_test). Nothing about when to call it is left to inference.

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