Sandbox API

dcc_mcp_core (sandbox module)

Script execution sandbox with API allowlist, path controls, audit logging, and input validation.

Overview

Enterprise users (game studios, VFX facilities) have strong security requirements that vanilla Python-based DCC MCP integrations cannot satisfy. The sandbox module provides:

• API allowlist — restrict which DCC actions an Agent may invoke
• Path allowlist — restrict filesystem access to safe directories
• Audit log — structured record of every action invocation (AuditEntry / AuditLog)
• Input validation — field-level rules with injection guards (InputValidator)
• Read-only mode — Agent can query but not mutate the scene

SandboxPolicy

Security policy configuration for a sandbox session.

Constructor

from dcc_mcp_core import SandboxPolicy

policy = SandboxPolicy()

Methods

Method	Returns	Description
allow_actions(actions)	None	Restrict execution to only these actions (replaces previous allowlist)
deny_actions(actions)	None	Deny these actions even if on the allowlist
allow_paths(paths)	None	Allow filesystem access inside these directory paths
set_timeout_ms(ms)	None	Set execution timeout in milliseconds
set_max_actions(count)	None	Set max number of actions allowed per session
set_read_only(read_only)	None	Enable/disable read-only mode

Properties

Property	Type	Description
is_read_only	bool	Whether policy is in read-only mode

Example

policy = SandboxPolicy()
policy.allow_actions(["get_scene_info", "list_objects", "get_object_info"])
policy.deny_actions(["delete_scene", "delete_object"])
policy.allow_paths(["/studio/assets", "/tmp/renders"])
policy.set_timeout_ms(5000)
policy.set_max_actions(100)
policy.set_read_only(False)

print(policy.is_read_only)  # False

Use allowlists, not denylists

Start with no actions allowed, then explicitly permit safe ones. This is more secure than listing everything you want to block.

SandboxContext

Main sandbox execution context. Bundles a SandboxPolicy with an AuditLog and an action counter.

Constructor

from dcc_mcp_core import SandboxPolicy, SandboxContext

policy = SandboxPolicy()
policy.allow_actions(["get_scene_info", "list_objects"])

ctx = SandboxContext(policy)

Methods

Method	Returns	Description
set_actor(actor)	None	Set caller identity for audit entries
execute_json(action, params_json)	str	Execute action with JSON params, returns JSON result
is_allowed(action)	bool	Check if action is permitted by current policy
is_path_allowed(path)	bool	Check if path is within an allowed directory

Properties

Property	Type	Description
action_count	int	Number of actions successfully executed
audit_log	AuditLog	The audit log for this context

Execution

ctx.set_actor("claude-agent")

# Execute with JSON params — returns JSON string
result = ctx.execute_json("get_scene_info", "{}")
print(result)  # '{"name": "my_scene", "object_count": 42, ...}'

# Check permissions without executing
if ctx.is_allowed("delete_object"):
    ctx.execute_json("delete_object", '{"name": "pSphere1"}')

Errors raise RuntimeError

execute_json() raises RuntimeError if the action is denied, validation fails, or a sandbox error occurs.

Audit Log Access

log = ctx.audit_log
print(len(log))  # number of recorded entries

for entry in log.entries():
    print(f"{entry.actor}: {entry.action} → {entry.outcome} ({entry.duration_ms}ms)")

# Filtered views
denied = log.denials()
succeeded = log.successes()

# Serialize to JSON
json_str = log.to_json()

AuditEntry

A single audit record for one action invocation. All attributes are read-only properties.

Properties

Property	Type	Description
timestamp_ms	int	Unix timestamp in milliseconds
actor	str | None	Caller identity, or None
action	str	Action name
params_json	str	Parameters as JSON string
duration_ms	int	Execution duration in milliseconds
outcome	str	"success", "denied", "error", or "timeout"
outcome_detail	str | None	Denial reason or error message, or None

for entry in ctx.audit_log.entries():
    print(f"[{entry.timestamp_ms}] {entry.actor}: {entry.action}")
    print(f"  params: {entry.params_json}")
    print(f"  outcome: {entry.outcome} ({entry.duration_ms}ms)")
    if entry.outcome_detail:
        print(f"  detail: {entry.outcome_detail}")

AuditLog

Read-only view of the sandbox audit log.

Methods

Method	Returns	Description
entries()	list[AuditEntry]	All recorded entries
successes()	list[AuditEntry]	Entries with outcome "success"
denials()	list[AuditEntry]	Entries with outcome "denied"
entries_for_action(action)	list[AuditEntry]	Entries for a specific action
to_json()	str	All entries serialized as a JSON array
__len__()	int	Number of entries

log = ctx.audit_log

print(f"Total: {len(log)}")
print(f"Successes: {len(log.successes())}")
print(f"Denials: {len(log.denials())}")

# All scene_info queries
scene_queries = log.entries_for_action("get_scene_info")

# Export for logging system
import json
entries_json = log.to_json()

InputValidator

Field-level input validator with injection guards. Use to validate parameters before passing to SandboxContext.execute_json().

Constructor

from dcc_mcp_core import InputValidator

validator = InputValidator()

Methods

Method	Returns	Description
require_string(field, max_length=None, min_length=None)	None	Register a required string field with optional length bounds
require_number(field, min_value=None, max_value=None)	None	Register a required numeric field with optional range
forbid_substrings(field, substrings)	None	Injection guard: field must not contain any listed substring
validate(params_json)	tuple[bool, str | None]	Validate JSON params; returns (True, None) or (False, error)

Example

from dcc_mcp_core import InputValidator

validator = InputValidator()

# Field constraints
validator.require_string("name", min_length=1, max_length=64)
validator.require_number("radius", min_value=0.01, max_value=1000.0)

# Injection guards
validator.forbid_substrings("script", ["__import__", "exec(", "eval(", "os.system"])

# Valid input
ok, error = validator.validate('{"name": "sphere1", "radius": 2.0}')
print(ok, error)  # True, None

# Injection attempt blocked
ok, error = validator.validate('{"script": "__import__(os)"}')
print(ok, error)  # False, "field 'script' contains forbidden substring '__import__'"

# Runtime error on invalid JSON
try:
    validator.validate("not json")
except RuntimeError as e:
    print(f"Invalid JSON: {e}")

validate() vs ToolValidator

InputValidator is for sandbox field-level rules (length, range, injection guards). ToolValidator (from the actions module) validates against a JSON Schema. Use InputValidator inside a sandbox; use ToolValidator at the tool dispatch layer.

Best Practices

1. Always use allowlists — Start with no actions allowed, then explicitly permit safe ones
2. Set timeouts — Prevent runaway scripts from hanging the DCC
3. Limit action counts — set_max_actions() prevents runaway agent loops
4. Enable audit logging — Always inspect ctx.audit_log after a session
5. Use read-only mode — Enable when only querying data to prevent accidental mutations
6. Add injection guards — Use InputValidator.forbid_substrings() for any script/code parameters
7. Validate paths — Use allow_paths() + ctx.is_path_allowed() to prevent path traversal

Full Example

from dcc_mcp_core import SandboxPolicy, SandboxContext, InputValidator

# Build policy
policy = SandboxPolicy()
policy.allow_actions(["get_scene_info", "list_objects", "run_script"])
policy.allow_paths(["/studio/assets"])
policy.set_timeout_ms(10000)
policy.set_max_actions(50)

# Build validator for run_script
validator = InputValidator()
validator.require_string("script", max_length=10000)
validator.forbid_substrings("script", [
    "__import__", "exec(", "eval(", "os.system", "subprocess",
])

# Create context
ctx = SandboxContext(policy)
ctx.set_actor("my-ai-agent")

# Execute a safe read query
result = ctx.execute_json("get_scene_info", "{}")
print(result)

# Attempt a potentially dangerous action (blocked by policy)
try:
    ctx.execute_json("delete_scene", "{}")
except RuntimeError as e:
    print(f"Blocked: {e}")

# Review audit log
for entry in ctx.audit_log.entries():
    print(f"{entry.action}: {entry.outcome}")