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

Discloses behavior well beyond the annotations: the exact response envelope, the ORIGIN_NOT_ALLOWED no-capture path, the debugger-detach fallback, CAPTURE_PERMISSION_MISSING remediation, the fact that a failed screenshot does not consume screenshotsRemaining, and RATE_LIMITED with retryAfterMs. These are concrete operational facts an agent cannot infer from readOnlyHint/idempotentHint alone.

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?

Front-loaded with the return format, which is what an agent most needs, and every sentence carries an error-path or capacity fact. It is dense and slightly crammed into one block, but there is little filler.

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 specifies the return values and error semantics, which is the important gap to close. The remaining hole is parameter meaning for a 2-parameter tool, which leaves it short of complete.

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% and neither parameter is explained. sessionId is only obliquely implied by 'shared tab,' and the 'reason' field is never mentioned at all, so the description does not compensate for the schema gap.

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 (returns a JPEG of the visible shared tab) and specifies the exact return shape: MCP image content plus a small JSON text part with observationId, width, height. This is precise enough to distinguish it from browser_observe, which is not an image-returning tool.

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?

Gives clear preconditions: capture only runs when the tab origin is in allowedOrigins, site access for that origin is sufficient, and Chrome permission prompts require Enable or Reconnect. It doesn't explicitly compare against siblings like browser_observe or browser_get_status, so the when-not guidance is implied rather than named.

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