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

Annotations already declare readOnlyHint=true, but the description adds substantial behavioral context: allowlisted store requirement, demo/test-only behavior without auth, merchant-synced data fields, priceSource distinctions, and the warning 'Never quote price from memory.' This goes well beyond what annotations alone convey and does not contradict them.

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?

The description is dense and front-loaded with the core purpose, followed by auth, return fields, and guardrails. It is longer than minimal, but nearly every sentence adds operational value for an agent; the long tail of 'Never' instructions is justified by high-stakes pricing behavior.

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 fully enumerates the returned fields, including edge cases like priceSource (feed|live) and the always-present url/trackedUrl/pick. It also covers the auth lifecycle, required identifiers, and an example trigger list. An agent has enough to call it correctly and interpret the result.

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 only 50%, but the description compensates for all four parameters. It clarifies product_id and store_id as the lookup key, explains that q is the owner's search phrase for pick.whyRu, and elaborates on sessionId for authenticated retries. The meaning added is precise and actionable for correct invocation.

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 names a specific verb and resource: 'Get one ProductCard by product_id + store_id from an allowlisted store.' It scopes the tool precisely and helps distinguish it from siblings like search_products or peek_stores. The first sentence alone tells an agent exactly what this tool does and on what identifiers.

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 explicit when-to-use context with trigger phrases, explains the auth prerequisite for live data via begin_agent_link/OAuth, and tells the agent to call this before create_purchase. It also gives hard exclusions like 'Never web-search' and 'Never begin_agent_link again' when a sessionId already exists, which is actionable routing guidance.

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