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

Beyond the destructiveHint annotation, the description reveals failure modes (topic not existing, old not found, multiple occurrences without replace_all) and the side effect of bumping the 'updated' timestamp. This is rich behavioral context not present in annotations.

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 five tightly written sentences with no fluff. The first sentence defines the core purpose, and each subsequent sentence provides essential failure, side-effect, or alternative information. Nothing is redundant.

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?

Given an output schema is present, there is no need to explain return values. The description covers purpose, exact behavior, failure modes, side effects, and alternative sibling tools, making it fully adequate for a tool of this complexity.

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 baseline is 3. The description adds value by contextualizing parameters: e.g., it explains that 'old' appearing more than once causes failure if replace_all is false, which connects parameter semantics to runtime behavior. This is beyond what the schema states.

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 'Exact-string replacement inside an existing topic' with a specific verb and resource, and distinguishes itself from siblings by explicitly directing metadata changes to write. This is 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?

It provides explicit when-to-use guidance ('Exact-string replacement') and an explicit alternative for metadata changes ('To change title, tags, or expiry, use write instead'). It also lists failure conditions that effectively say when not to use without replace_all, aiding correct tool selection.

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