MCP Tool Reference Medium Risk

write_custom_semgrep_rule

Provide guidance for creating Semgrep rules

Part of the Semgrep MCP server. Enforce policies on this tool with Intercept, the open-source MCP proxy.

semgrep/mcp Write

WHEN AI AGENTS USE THIS TOOL

AI agents use write_custom_semgrep_rule to create or modify resources in Semgrep. Write operations carry medium risk because an autonomous agent could trigger bulk unintended modifications. Rate limits prevent a single agent session from making hundreds of changes in rapid succession. Argument validation ensures the agent passes expected values.

WHY ENFORCE A POLICY ON WRITE_CUSTOM_SEMGREP_RULE

Without a policy, an AI agent could call write_custom_semgrep_rule repeatedly, creating or modifying resources faster than any human could review. Intercept's rate limiting ensures write operations happen at a controlled pace, and argument validation catches malformed or unexpected inputs before they reach Semgrep.

RECOMMENDED POLICY

Write tools can modify data. A rate limit prevents runaway bulk operations from AI agents.

semgrep.yaml 
tools:
  write_custom_semgrep_rule:
    rules:
      - action: allow
        rate_limit:
          max: 30
          window: 60

See the full Semgrep policy for all 8 tools.

DETAILS

Tool Name

write_custom_semgrep_rule

Category

Write

MCP Server

Semgrep MCP Server

Risk Level

Medium

MORE SEMGREP TOOLS

get_abstract_syntax_tree Read
Output the Abstract Syntax Tree of code
security_check Other
Scan code for security vulnerabilities
semgrep_findings Other
Fetch findings from the Semgrep AppSec Platform API
semgrep_rule_schema Other
Fetch the latest Semgrep rule JSON Schema
semgrep_scan Other
Scan code files with a given config string
semgrep_scan_with_custom_rule Other
Scan code files using a custom Semgrep rule
supported_languages Other
Return the list of languages Semgrep supports

SIMILAR WRITE TOOLS ON OTHER SERVERS

create_table Airtable
Create a new table with fields
update_table Airtable
Update a table's name or description
create_field Airtable
Add a new field to a table
update_field Airtable
Modify an existing field
create_record Airtable
Add a new record
update_record Airtable
Modify an existing record

RELATED READING

FREQUENTLY ASKED QUESTIONS

What does the write_custom_semgrep_rule tool do?

Provide guidance for creating Semgrep rules. It is categorised as a Write tool in the Semgrep MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on write_custom_semgrep_rule?

Add a rule in your Intercept YAML policy under the tools section for write_custom_semgrep_rule. You can allow, deny, rate-limit, or validate arguments. Then run Intercept as a proxy in front of the Semgrep MCP server.

What risk level is write_custom_semgrep_rule?

write_custom_semgrep_rule is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.

Can I rate-limit write_custom_semgrep_rule?

Yes. Add a rate_limit block to the write_custom_semgrep_rule rule in your Intercept policy. For example, setting max: 10 and window: 60 limits the tool to 10 calls per minute. Rate limits are tracked per agent session and reset automatically.

How do I block write_custom_semgrep_rule completely?

Set action: deny in the Intercept policy for write_custom_semgrep_rule. The AI agent will receive a policy violation error and cannot call the tool. You can also include a reason field to explain why the tool is blocked.

What MCP server provides write_custom_semgrep_rule?

write_custom_semgrep_rule is provided by the Semgrep MCP server (semgrep/mcp). Intercept sits as a proxy in front of this server to enforce policies before tool calls reach the server.

ENFORCE POLICIES ON SEMGREP

Open source. One binary. Zero dependencies.

VIEW ON GITHUB Full Semgrep policy →