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

With annotations already covering the read-only/idempotent safety profile, the description adds substantive behavior: per-statistic minimum sample sizes (t/dz ≥ 3, Wilcoxon ≥ 5), a large base64 PNG return with guidance to render or save it, and a graceful empty-payload-instead-of-error contract that an agent needs to reason about output.

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 deliverable is front-loaded ('Paired pre/post analysis for one assignment') with details following. It is dense and clause-heavy with several parentheticals, but each clause conveys actionable information (minimums, figure format, empty-payload behavior) rather than 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?

For a tool that also has an output schema, the description is more than sufficient: it characterizes the payload contents, documents the statistical minimums, and explicitly resolves the empty-assignment case. Nothing an agent needs to invoke or interpret the call 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 coverage is 100% and the single parameter is already documented in-schema ('from start_assignment'), so the schema carries the meaning. The description ties the analysis to 'one assignment' but adds no syntax or format detail beyond what the schema provides, matching the baseline for a fully documented single param.

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?

Names a specific analysis type (paired pre/post) scoped to one assignment's recorded sessions, and enumerates exactly what it produces (per-block aggregates, t/Wilcoxon/dz, trajectory, figure). The verb+resource is crystal clear, though it does not explicitly distinguish itself from the nearest sibling, stats.grouped.

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?

The intent (paired pre/post comparison for a single assignment) is implied by the content, and the edge case of an assignment with no recordings is noted, but there is no explicit 'use this when X, use stats.grouped when Y' routing guidance or prerequisites beyond the parameter's own note.

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