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

Annotations already declare readOnlyHint, idempotentHint and destructiveHint=false, so the safety profile is covered; the description adds genuinely new facts beyond them — "Pure text analysis, nothing stored" (no persistence side effects) and the 1024 code point ceiling. It also notes engine parity with POST /api/compare. It stops short of 5 only because nothing is said about error behavior for invalid input.

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?

Front-loaded with the core action and the possible verdicts, then the auxiliary outputs, then constraints and behavioral notes — a sensible order with little waste. The trailing "Same engine as POST /api/compare" sentence is the one item of marginal value for an MCP agent.

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?

An output schema exists, so return values need not be spelled out, yet the description still enumerates the verdict categories and extra fields (scripts, mixed-script flag, skeleton). Inputs, size limits, side-effect profile and API parity are all covered; nothing needed to invoke it correctly is missing.

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% and both parameters already carry examples and min/maxLength, so the schema does the heavy lifting; this is the baseline. The description reinforces the 1024 limit and hints at the trusted-vs-received framing, but adds no syntax or normalization detail beyond the schema.

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 and resource ("Compare two strings") and names the exact mechanism and outcome set (UTS #39 skeletons; identical/confusable/confusable_ignoring_case/distinct), so the agent knows precisely what it gets back. It never names the sibling scan_text or explains how the two differ, so it stops short of the top band.

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?

Parenthetical examples ("usernames, domains, brand or command names") imply the phishing/look-alike-check scenario but never frame it as explicit when-to-use guidance, and there is no routing advice versus scan_text. Usage is inferable rather than stated.

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