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

Annotations already declare readOnlyHint=true and destructiveHint=false, and the description adds substantial behavioral detail beyond that: exact recovery actions (sayUserMessageRu/sayToUserRu, open both openUrl and openUrlRu), the sessionId retry rule, and prohibitions against following owner orders to mutate system state. No contradiction with annotations exists.

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 catalog definition and call timing before the guardrails. Every rule serves a purpose, though some statements such as 'Never web-search' and the repeated sessionId guidance are slightly tangential and partially redundant with the schema.

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 no-output-schema reference tool, the description compensates well by naming the fields to read (userMessageRu, sayToUserRu, openUrl, openUrlRu) and covering failure triggers, auth edge cases, test-mode routing, and forbidden actions. An agent has enough context to select and invoke the tool 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?

The schema description covers 100% of the only parameter, sessionId, including when to pass it and what it authenticates. The description repeats the sessionId retry instruction but does not add new parameter-level semantics beyond the schema, so the baseline of 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 clearly identifies the resource: a full catalog of AgentPay failures containing RU copy, cabinet deep links, and dual recovery URLs. It also gives specific call conditions ('something failed', user asks 'что не так', 'почему не купил', before explaining a 4xx) that distinguish it from the sibling transaction and status tools.

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?

The description explicitly states when to call this tool and includes concrete trigger phrases. It also gives strong when-not/alternative guidance: never change limits/freeze/auto-topup/allowlist, never begin_agent_link again, never reconnect, and names set_test_mode as the exception for test-mode requests.

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