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

Annotations already declare readOnly/idempotent/non-destructive, so the description is free to add real value — and it does: it discloses that secrets are never returned ('Never returns a key itself') and that browser_sessions reflects live signed-in browsers that revoking the key would sign out. That cross-tool consequence is context an agent could not infer from structured fields.

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?

A single dense sentence, front-loaded with the resource and the field inventory, ending with the most important safety caveat. It is slightly run-on with the parenthetical definitions, but every clause carries information.

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's field glossary resolves the ambiguity between 'agent' and 'key' that the schema alone would not. Together with the no-secret-leak note, an agent has everything needed to call and interpret it.

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?

The tool takes zero parameters, so there is nothing for the description to disambiguate; the baseline of 4 applies. No misleading parameter claims are made.

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 ('List the agents connected to your account') and immediately disambiguates the vocabulary by explaining that 'agents' means API keys with id, name, timestamps. It doesn't explicitly name the sibling key_revoke as the alternative, but the read/list framing makes the distinction obvious.

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 is implied: this is the inventory call for inspecting connected agents. There is no explicit 'use this when' or 'do not use this for' statement, and no mention of when to prefer whoami or key_revoke instead, though the tool takes no parameters so misuse risk is low.

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