reaches

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

With no annotations provided, the description carries the full burden and does so excellently. It discloses the operation is read-only, describes the output (labeled witness path or honest negative), explains the truncation caveat, and clarifies the exact edge semantics. This goes well beyond a typical tool description.

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 compact and front-loaded: it opens with 'Read-only' and the core question, then adds essential caveats and usage guidance. Every sentence earns its place, and there is no redundant or filler content.

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?

Despite having no output schema or annotations, the description gives an agent enough to use the tool correctly: purpose, output nature, edge-set semantics, truncation limitation, and sibling alternatives. It anticipates the most likely confusions, making it complete for this analysis-oriented tool.

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 the baseline holds; the schema already documents `src`, `sink`, and `format`. The description adds contextual meaning by framing the parameters as a specific source->sink pair, but it does not add significant semantic detail beyond what the schema provides.

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 clearly states the tool's function: it checks whether a source reaches a sink through value flow and returns a labeled witness path or a negative. It also distinguishes itself from siblings by naming the specific edge set and contrasting with `flow`/`sources_of` and `taint`.

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 explicitly says when to use this tool ('confirm one specific source->sink pair') and when not to ('use `flow`/`sources_of` to explore a whole cone'). It also warns that `reaches` follows VALUE_FLOWS_TO/POINTS_TO rather than the taint edge set, preventing misuse.

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