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

With no annotations, the description carries full responsibility for behavioral disclosure. It does disclose one trait: 'Query discarded' indicates the input is not retained or returned. But it says nothing about what the tool returns (a number? a status?), how it handles the other eight parameters, what happens if multiple parameters are provided, or whether the operation is read-only. These gaps are significant for a tool with such a broad parameter surface.

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 consists of two short sentences with no filler. The primary purpose is front-loaded, and the second sentence adds a useful behavioral note without redundancy. Every word contributes meaning, making it an excellent example of conciseness.

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 a 9-parameter schema, no output schema, and no annotations, the description offers only a bare statement about counting characters in a search query. It does not explain the relationship among the 9 parameters, which one is the 'search query,' whether they are mutually exclusive, what the return shape is, or what side effects occur. An agent would be left guessing how to call the tool correctly for anything other than the simplest single-query use case.

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 is 3. The tool description adds no parameter-specific value beyond reinforcing that the 'query' parameter is a search text that gets discarded. It does not clarify whether the other parameters are alternatives, ignored, or also subject to counting. Since the schema already documents each parameter's own role, the description neither improves nor detracts from parameter understanding.

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 and resource: 'Count characters in a search query.' This clearly distinguishes the core action from sibling count tools like memory-key-count or hn-front-count. However, the schema exposes 8 additional parameters (URL, city, feed, host, JSON, path, zone) that are not mentioned in the description, leaving ambiguity about whether the tool can also operate on those inputs. Thus it is clear but not fully unambiguous.

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 implies when to use the tool: when you need the character count of a search query. But it provides no explicit guidance about alternatives, no exclusions, and no mention of when to prefer another tool. The sibling list includes several shape/check tools, but the description does not address them. Usage must be inferred from the purpose statement rather than being explicitly stated.

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