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

Annotations already mark readOnly/idempotent/non-destructive, and the description adds substantial behavior: traversal over edges, provenance data (which CO reached it, edge source, note), response kinds ({kind: 'evidenced', value, chain} or {kind: 'no_evidence_available'}), and parameter defaults. This goes well beyond what annotations provide, with no contradiction.

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 description is mostly tightly structured and front-loaded with the core purpose, but it has redundancy: the final 'Returns: The set of surfaces a change reaches.' repeats the earlier response-shape sentence, and the example 'call introspection_system_change_reach with arguments {}' is empty and unhelpful. Every sentence does not fully earn its place.

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?

Given the tool's complexity (graph traversal, provenance, evidence chain, parameter defaults, and no output schema), the description covers all necessary input semantics, defaults, output shapes, and behavioral details. It is complete enough for an agent to invoke correctly, with only minor undefined jargon (CO, D8) that is acceptable in context.

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 0%, so the description fully compensates by explaining each parameter: origin_slug is the CO directory slug with an example, max_hops bounds traversal depth (default 1), and include_parent_child toggles decomposition tree reach (default true). This gives meaning beyond the raw schema.

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 uses a specific verb 'Return' with a clear resource 'REACH of a change' and defines scope: 'every artifact across every registered repo' traversed over the change-graph's interest + parent/child edges. This distinguishes it from sibling tools like change_graph (which likely returns the graph) and list_nodes (which lists nodes), making the purpose unmistakable.

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?

It provides clear context on what the tool computes (the reach of a change, surfaces affected) and explains key parameters and defaults (max_hops, include_parent_child). However, it does not explicitly name alternatives or state when-not-to-use it, which would be needed for a 5.

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