nexus_read_span

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

Annotations already declare readOnlyHint=true and idempotentHint=true, indicating a safe read operation. The description adds valuable behavioral context beyond annotations by mentioning 'Encoding-safe, binary-aware, injection-scanned,' which alerts the agent to how the tool handles file contents and security checks. No contradictions exist.

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 exceptionally concise, using two short sentences. It front-loads the primary purpose and then adds three key behavioral traits in a compact tagline. Every word earns its place with zero redundancy.

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 simple read tool with annotations covering safety, the description covers the core purpose and some behavioral traits. However, with four parameters, no output schema, and minimal schema coverage, it leaves important gaps: the semantics of start, end, and allowSensitive are not explained, nor is the return format. It is adequate but not fully complete.

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?

Input schema description coverage is only 25% (only 'file' is described). The phrase 'line range' loosely implies start and end are line numbers, but the description does not explicitly explain the parameters or their defaults, and 'allowSensitive' is entirely unexplained. The description fails to compensate for the low schema coverage.

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 a specific operation: 'Read a line range of a file.' This distinctly identifies the tool's purpose and differentiates it from sibling tools like nexus_search or nexus_file_symbols, which focus on other actions.

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 description provides no guidance on when to use this tool compared to alternatives. It does not mention any exclusions, prerequisites, or scenarios where other tools would be more appropriate. The sibling list is extensive, but the description offers no decision support.

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