Rex CLI guide

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

With no annotations, the description carries the burden and does well: it discloses the payload size (~20 KB, relevant to context budget) and that content is returned verbatim rather than summarized. It stops short of stating explicitly that the operation is a safe read with no side effects, but 'Read' strongly implies it.

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 sentences, both earning their place: the first gives the payload and its size, the second gives the timing rule. The most actionable instruction is placed last for emphasis without burying the purpose.

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 zero-parameter, output-schema-less documentation fetch, the description supplies everything needed: what is returned, its approximate size, and when to invoke it. Nothing further is required to call it 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?

The tool takes zero parameters, so the baseline is 4 and there is nothing the description could add. It correctly spends no words on parameter explanation.

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 ('Read'), a specific resource (the installed Rex CLI guide), and the exact behavior ('verbatim, about 20 KB'). By naming the sibling 'rex', an agent can immediately tell this is the documentation lookup rather than the CLI executor.

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?

Explicitly says when to call it: 'Read this before the first rex call.' That is a clear ordering/context trigger relative to the only sibling, leaving nothing to inference about sequencing.

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