# Call Tools > Make HTTP API calls as agent tools. Call tools let agents interact with REST APIs directly — the agent sends a request and gets the response back. **URL:** https://inference.sh/docs/api/agent/call-tools **Last updated:** 2026-10-18 --- Make HTTP API calls as agent tools. Call tools let agents interact with REST APIs directly — the agent sends a request and gets the response back. --- ## Basic Usage Call tools are defined in the agent's YAML config: ```yaml tools: - name: get_weather type: call description: Get current weather for a city call: method: GET url: https://api.weather.com/v1/current?city={{args.city}} input_schema: type: object properties: city: type: string description: City name ``` When the agent calls `get_weather(city="London")`, the runtime makes a GET request to `https://api.weather.com/v1/current?city=London` and returns the response body as the tool result. --- ## How It Works 1. Agent decides to call the tool based on the conversation 2. Runtime substitutes `{{context.X}}` in the call's arguments, then resolves the URL template (`{{context.X}}`, `{{args.X}}`) and `{{context.X}}` in headers 3. Runtime injects auth credentials (headers, bearer token) 4. Request is sent and response is returned to the agent The agent never sees credentials — auth is handled entirely by the runtime. --- ## URL Templates URLs support two kinds of template variables: | Syntax | Source | Resolved when | |--------|--------|---------------| | `{{context.X}}` | Per-chat context values (set at chat creation) | Each tool call | | `{{args.X}}` | Tool call arguments | Each tool call | `{{args.X}}` values are consumed from the request body — they appear in the URL but are removed from the JSON body sent to the endpoint. ```yaml url: https://api.example.com/projects/{{context.project_id}}/items/{{args.item_id}} ``` --- ## Authentication Configure auth in the tool's `call.auth` section. Credentials come from your workspace's secrets (`belt secrets set`). ### Bearer Token ```yaml call: auth: type: bearer secret: my_api_key # workspace secret name method: GET url: https://api.example.com/data ``` Sends `Authorization: Bearer ` on every request. ### API Key Header ```yaml call: auth: type: api_key secret: my_api_key header: X-API-Key # custom header name method: POST url: https://api.example.com/action ``` ### Credential (OAuth) ```yaml call: auth: type: credential provider: google method: GET url: https://www.googleapis.com/calendar/v3/calendars/primary/events ``` Uses the runner's own connected credential for that provider. With none, the chat pauses and asks them to connect one. ### No Auth ```yaml call: auth: type: none method: GET url: https://api.example.com/public ``` Omitting `call.auth` entirely, or leaving `auth.type` empty, sends no credentials — the same behavior as `type: none`. Generated SDK types expose this as `ToolAuthTypeNone` / `ToolAuthType.NONE`. --- ## Input Schema Define the tool's parameters with `input_schema`. This becomes the JSON Schema the LLM sees: ```yaml call: method: POST url: https://api.example.com/search input_schema: type: object properties: query: type: string description: Search query limit: type: integer description: Max results to return filters: type: object description: Key-value filter pairs ``` For `POST`/`PUT` requests, the input schema fields become the JSON request body (minus any `{{args.X}}` values consumed by the URL). For `GET`/`DELETE` requests, parameters can be embedded in the URL via `{{args.X}}` templates. --- ## Require Approval For destructive or expensive operations: ```yaml tools: - name: delete_record type: call description: Permanently delete a record require_approval: true call: auth: type: bearer secret: admin_key method: DELETE url: https://api.example.com/records/{{args.id}} input_schema: type: object properties: id: type: string description: Record ID to delete ``` The agent pauses and waits for user confirmation before executing. --- ## Context Call tools work with agent context — per-chat variables declared in the agent config and passed when creating a chat. ```yaml # Agent config context: - name: project_id description: Project to operate on required: true tools: - name: list_tasks type: call description: List tasks in the project call: auth: type: bearer secret: pm_api_key method: GET url: https://api.example.com/projects/{{context.project_id}}/tasks ``` Pass context when running the agent: ```bash belt agent run myteam/pm-agent "list open tasks" \ --context project_id=proj_123 ``` --- ## Full Example A pricing configuration agent with multiple call tools: ```yaml name: pricing-agent description: Configure pricing for store apps core_app: ref: openrouter/claude-sonnet-45 context: - name: version_id description: Store version ID required: true tools: - name: get_pricing type: call description: Returns current pricing state call: auth: type: bearer secret: api_key method: GET url: https://api.example.com/versions/{{context.version_id}}/pricing - name: save_draft type: call description: Save pricing config as draft call: auth: type: bearer secret: api_key method: PUT url: https://api.example.com/versions/{{context.version_id}}/pricing/draft input_schema: type: object properties: prices: type: object description: Price variables (name to value in cents) total_expression: type: string description: CEL expression for total fee - name: publish type: call description: Promote draft to live pricing require_approval: true call: auth: type: bearer secret: api_key method: POST url: https://api.example.com/versions/{{context.version_id}}/pricing/publish ```