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

With no annotations, the description carries the full burden of behavioral disclosure. It does add value: 'using a real regex engine' signals genuine evaluation rather than a mock or heuristic check, and the return behavior (all matches, capture groups, indices) is stated. However, it omits error behavior for invalid patterns, how flags alter matching, and any explicit statement that the operation has no side effects.

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, roughly 30 words, with zero filler. The action is front-loaded, and both sentences earn their place: the first states what it does, the second states what it returns. 'Using a real regex engine' is non-redundant because it distinguishes genuine evaluation from simulation.

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 moderately simple tool with no output schema and no annotations, the description covers purpose, main parameters, and return shape. Gaps remain: the flags parameter is unexplained, error handling for invalid regex patterns is unspecified, and the structure of returned matches/indices is only vaguely described. Adequate for invocation but not exhaustive.

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 must compensate. It maps 'regular expression' to pattern and 'test string' to text, adding real meaning for two of three parameters. But the flags parameter is never mentioned, even though the description's claim of returning 'all matches' depends on the default 'g' flag — leaving an agent to guess at flag semantics.

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 states a specific verb ('Run') and resource ('a JavaScript regular expression against a test string'), with a clear behavioral qualifier ('using a real regex engine'). It also specifies the return value: all matches with capture groups and indices. None of the 35 sibling tools perform regex testing, so it stands clearly apart.

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?

Usage context is implied: an agent would select this tool when it needs to evaluate a regex against sample text. However, there is no explicit when-to-use/when-not-to-use guidance, no exclusions, and no mention of alternative tools. The absence of a regex sibling lowers the stakes, but the description still leaves the decision entirely to inference.

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