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

Annotations already cover the safety profile (readOnlyHint=false, destructiveHint=false, openWorldHint=false), so the description's added value is the failure contract — already_exists plus data.existing_label_id in the error payload — and the semantic restriction that the created label can never be an AI send-block or AI-protected label. That is real behavior beyond the structured fields; only the idempotentHint nuance (a repeat call fails rather than no-ops) is left implicit.

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?

Three short sentences, front-loaded with purpose and constraints, each carrying information. The final sentence on AI label exclusion is a niche caveat but earns its place by preventing a wrong assumption about what gets created.

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?

For a three-parameter mutation with an output schema (so return values need no explanation) and full annotation coverage, this is nearly complete. The gaps are the undocumented 'description' parameter and the name-length bound, both of which the schema states only structurally.

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 0%, so the description must carry the parameter burden. It does explain name uniqueness and that color is a palette index 0-9 (the schema only gives min/max 0-9 without meaning), but it says nothing about the third parameter, 'description', nor about the 80-character name limit.

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 opens with a specific verb+resource ('Create a new label') and immediately bounds it with two constraints (org-unique name, color as a 0-9 palette index). It is clearly distinct from the list_labels and update_labels siblings, though it never names them explicitly.

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 rather than stated: the agent learns that duplicate names are rejected with already_exists, which tells it to check existence first, but the description never says when to call this versus update_labels or how to recover (it does point at data.existing_label_id). No explicit alternatives or preconditions are given.

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