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

With no annotations, the description carries the behavioral burden. It clearly discloses what the tool does and returns, including a useful parenthetical on headless-readiness. It does not explicitly state read-only/no-write behavior or failure modes, but its comparison semantics make the side-effect profile clear.

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, front-loaded with purpose, then a compact list of return fields, then usage. The parenthetical explanation of headless-readiness earns its place; no fluff.

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?

With no output schema, the description compensates by enumerating the key return values and giving a concrete use case. It doesn't cover edge cases like uncatalogued tools or fuzzy-match failures, but the tool's simplicity and schema coverage make this a minor gap.

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 coverage is 100%, so the baseline is 3. The description adds GTM context and vendor examples, but does not materially expand on the parameter semantics already present in the input 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?

Description opens with a specific verb and resource: 'Head-to-head comparison of two GTM tools.' It enumerates distinctive outputs (cost delta, AI-readiness, headless-readiness, overlap, swap-registry, recommended pick), and the 'two' constraint plus examples separates it from siblings like compare_tools_n_way and find_overlaps.

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 states when to use: 'when the user is choosing between two specific vendors,' with concrete examples. It does not name alternative tools or state when not to use it, so it stops short of a full 5.

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