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Start Browser Test

start_session

Destructive

Launch a browser QA session at a URL with goals and constraints, returning the protocol, initial observation, and coverage so exploratory testing can begin.

Instructions

Start browser testing at url with goals and constraints. Returns the protocol, initial observation and coverage. Time budget is advisory. Does not grant authority for external effects.

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "url": "<url>"
    },
    "name": "start_session"
  }
}

Input Schema

Name	Required	Default
`url`	Yes
`goals`	No
`headless`	No
`constraints`	No
`review_mode`	No	exploratory
`viewport_width`	No
`viewport_height`	No
`include_observation`	No
`time_budget_minutes`	No

Output Schema

Name	Required	Description	Default
`data`	No
`run_id`	Yes
`stages`	No
`status`	Yes
`recovery`	No
`operation`	Yes
`error_code`	Yes
`session_state`	Yes
`schema_version`	No
`progress_omitted`	No
`progress_delivery_failed`	No

Schema Changelog

Changes observed during successful MCP inspections.

Changed10 schema fields changedv0.10.0Oct 26, 2026
- removedInput schema / properties / constraints / title
```
Removed value: -"Constraints"
```
- removedInput schema / properties / goals / title
```
Removed value: -"Goals"
```
- removedInput schema / properties / headless / title
```
Removed value: -"Headless"
```
- removedInput schema / properties / include_observation / title
```
Removed value: -"Include Observation"
```
- removedInput schema / properties / review_mode / title
```
Removed value: -"Review Mode"
```
- removedInput schema / properties / time_budget_minutes / title
```
Removed value: -"Time Budget Minutes"
```
- removedInput schema / properties / url / title
```
Removed value: -"Url"
```
- removedInput schema / properties / viewport_height / title
```
Removed value: -"Viewport Height"
```
- removedInput schema / properties / viewport_width / title
```
Removed value: -"Viewport Width"
```
- removedInput schema / title
```
Removed value: -"start_sessionArguments"
```
Changed12 schema fields changedOct 26, 2026
- removedOutput schema / properties / data / title
```
Removed value: -"Data"
```
- removedOutput schema / properties / error_code / title
```
Removed value: -"Error Code"
```
- removedOutput schema / properties / operation / title
```
Removed value: -"Operation"
```
- removedOutput schema / properties / progress_delivery_failed / title
```
Removed value: -"Progress Delivery Failed"
```
- removedOutput schema / properties / progress_omitted / title
```
Removed value: -"Progress Omitted"
```
- removedOutput schema / properties / recovery / title
```
Removed value: -"Recovery"
```
- removedOutput schema / properties / run_id / title
```
Removed value: -"Run Id"
```
- removedOutput schema / properties / schema_version / title
```
Removed value: -"Schema Version"
```
- removedOutput schema / properties / session_state / title
```
Removed value: -"Session State"
```
- removedOutput schema / properties / stages / title
```
Removed value: -"Stages"
```
- removedOutput schema / properties / status / title
```
Removed value: -"Status"
```
- removedOutput schema / title
```
Removed value: -"AgentResult"
```

Changed17 schema fields changedv0.5.2Oct 26, 2026

addedInput schema / properties / constraints

Added value: +{
+  "anyOf": [
+    {
+      "items": {
+        "type": "string"
+      },
+      "type": "array"
+    },
+    {
+      "type": "null"
+    }
+  ],
+  "default": null,
+  "title": "Constraints"
+}

addedInput schema / properties / goals

Added value: +{
+  "anyOf": [
+    {
+      "items": {
+        "type": "string"
+      },
+      "type": "array"
+    },
+    {
+      "type": "null"
+    }
+  ],
+  "default": null,
+  "title": "Goals"
+}

addedInput schema / properties / time_budget_minutes

Added value: +{
+  "default": 0,
+  "title": "Time Budget Minutes",
+  "type": "integer"
+}

addedOutput schema / properties / data

Added value: +{
+  "additionalProperties": true,
+  "title": "Data",
+  "type": "object"
+}

addedOutput schema / properties / error_code

Added value: +{
+  "anyOf": [
+    {
+      "type": "string"
+    },
+    {
+      "type": "null"
+    }
+  ],
+  "title": "Error Code"
+}

addedOutput schema / properties / operation

Added value: +{
+  "title": "Operation",
+  "type": "string"
+}

addedOutput schema / properties / progress_delivery_failed

Added value: +{
+  "default": false,
+  "title": "Progress Delivery Failed",
+  "type": "boolean"
+}

addedOutput schema / properties / progress_omitted

Added value: +{
+  "default": 0,
+  "title": "Progress Omitted",
+  "type": "integer"
+}

addedOutput schema / properties / recovery

Added value: +{
+  "items": {
+    "type": "string"
+  },
+  "title": "Recovery",
+  "type": "array"
+}

removedOutput schema / properties / result

Removed value: -{
-  "title": "Result",
-  "type": "string"
-}

addedOutput schema / properties / run_id

Added value: +{
+  "anyOf": [
+    {
+      "type": "string"
+    },
+    {
+      "type": "null"
+    }
+  ],
+  "title": "Run Id"
+}

addedOutput schema / properties / schema_version

Added value: +{
+  "const": 1,
+  "default": 1,
+  "title": "Schema Version",
+  "type": "integer"
+}

addedOutput schema / properties / session_state

Added value: +{
+  "title": "Session State",
+  "type": "string"
+}

addedOutput schema / properties / stages

Added value: +{
+  "items": {
+    "type": "string"
+  },
+  "title": "Stages",
+  "type": "array"
+}

addedOutput schema / properties / status

Added value: +{
+  "enum": [
+    "completed",
+    "error"
+  ],
+  "title": "Status",
+  "type": "string"
+}

changedOutput schema / required

Previous value: -[
-  "result"
-]New value: +[
+  "operation",
+  "status",
+  "session_state",
+  "run_id",
+  "error_code"
+]

changedOutput schema / title

Previous value: -"start_sessionOutput"New value: +"AgentResult"

Changed2 schema fields changedv0.5.1Jul 21, 2026

addedInput schema / properties / include_observation

Added value: +{
+  "default": true,
+  "title": "Include Observation",
+  "type": "boolean"
+}

addedInput schema / properties / review_mode

Added value: +{
+  "default": "exploratory",
+  "title": "Review Mode",
+  "type": "string"
+}

First observedv0.4.0Apr 27, 2026

TDQS

B3.1/5.0

Behavior3/5

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

Annotations already declare destructive=true, idempotent=false and openWorld=true, so the safety profile is largely covered. The description adds two genuinely useful bits — 'Time budget is advisory' and 'Does not grant authority for external effects' — but it never explains what the destructive/non-idempotent behavior means in practice (e.g., whether an existing session is discarded on a repeat call).

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Three tight sentences with the core action front-loaded and no filler. The return-value sentence is partly redundant given an output schema exists, which keeps it from a 5.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness2/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a 9-parameter session-initialization tool flagged destructive and non-idempotent, the description leaves most parameters and the repeat-call behavior undocumented. The output schema covers return shape, so that gap is excusable, but the parameter and teardown gaps are not.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters2/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 0% across 9 parameters, so the description must carry the burden and does not. It only alludes to url, goals, constraints and (via 'advisory') time_budget_minutes; headless, review_mode (what values beyond the 'exploratory' default?), viewport_width/height and include_observation are entirely unexplained.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose4/5

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb and resource ('Start browser testing at url') with the key inputs (goals, constraints) named. It is clearly the entry-point sibling to end_session/navigate, though it never names those siblings explicitly to draw the boundary.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines3/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The phrasing 'Start browser testing' implies this is the first call before other session tools, but there is no explicit when-to-use/when-not or routing to alternatives such as end_session for teardown or navigate for in-session movement. Usage is inferred rather than stated.

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