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

Annotations already cover the safety profile (idempotentHint=true, destructiveHint=false), so the bar is lower, yet the description adds merge semantics ('custom fields are merged; tags are additive') and the return shape ('returns the contact and a created boolean'). The merge/tag behavior partly overlaps the schema field descriptions, but the return-value disclosure is genuinely additive given there is no output schema.

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 tight sentences with the core create-or-update behavior front-loaded, followed by the differentiator and return contract. Every sentence earns its place with no redundancy.

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?

Despite eight parameters and no output schema, the description covers the conditional behavior, merge/tag semantics, and return value, and the schema fully documents the parameters. An agent has everything needed to invoke and interpret the result correctly.

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 all eight parameters are already documented in the schema. The description only restates the email key and adds no syntax or format detail beyond what the schema provides, so the baseline 3 applies.

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 states a specific compound verb (create-or-update = upsert) and resource (contact), and defines the exact selection key ('one with this email'). It distinguishes itself from the sibling meisa_add_contact/meisa_update_contact by explaining the conditional create/update behavior, so an agent can tell what it does without opening the schema.

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 gives clear context for when to reach for this tool ('the safest way to add or sync a contact without worrying about duplicates'), which implies preference over add_contact for sync scenarios. However, it never explicitly names the alternative tools or states when NOT to use it, so routing is inferred rather than directed.

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