api-context

Overview

Every tool and resource handler receives a single Context (ctx) argument. It provides request identity, structured logging, tenant-scoped storage, optional protocol capabilities (elicitation, sampling), cancellation, and task progress — all auto-correlated to the current request.

The framework auto-instruments every handler call (OTel span, duration, payload metrics). Use ctx.log for domain-specific logging and ctx.state for storage inside handlers. Use the global logger and StorageService directly only in lifecycle/background code (setup(), services).

---

Context interface

import type { Context } from '@cyanheads/mcp-ts-core';

interface Context {
  // Identity & tracing
  readonly requestId: string;       // Unique per request, auto-generated
  readonly timestamp: string;       // ISO 8601 request start time
  readonly tenantId?: string;       // From JWT 'tid' claim; 'default' in stdio mode
  readonly traceId?: string;        // OTEL trace ID (present when OTEL enabled)
  readonly spanId?: string;         // OTEL span ID (present when OTEL enabled)
  readonly auth?: AuthContext;      // Parsed auth claims (clientId, scopes, sub)

  // Structured logging — auto-includes requestId, traceId, tenantId
  readonly log: ContextLogger;

  // Tenant-scoped key-value storage
  readonly state: ContextState;

  // Optional protocol capabilities (undefined when client doesn't support them)
  readonly elicit?: (message: string, schema: z.ZodObject<z.ZodRawShape>) => Promise<ElicitResult>;
  readonly sample?: (messages: SamplingMessage[], opts?: SamplingOpts) => Promise<CreateMessageResult>;

  // Cancellation
  readonly signal: AbortSignal;

  // Task progress — present only when tool is defined with task: true
  readonly progress?: ContextProgress;

  // Raw URI — present only for resource handlers
  readonly uri?: URL;
}

Identity fields

Field	Always present	Source
requestId	Yes	Auto-generated UUID per request
timestamp	Yes	ISO 8601, request start
tenantId	In stdio (as 'default'); from JWT tid claim in HTTP	JWT / stdio default
traceId	When OTEL enabled	OTEL trace context
spanId	When OTEL enabled	OTEL trace context
auth	When auth enabled	Parsed JWT claims

---

ctx.log

Request-scoped structured logger. Every log line is automatically annotated with requestId, traceId, and tenantId — no manual spreading needed.

Methods

Method	Level
ctx.log.debug(msg, data?)	Verbose debugging
ctx.log.info(msg, data?)	Normal operational events
ctx.log.notice(msg, data?)	Significant but non-error events
ctx.log.warning(msg, data?)	Recoverable issues, unexpected states
ctx.log.error(msg, error?, data?)	Errors (second arg is the Error object)

Usage

// Basic
ctx.log.info('Processing query', { query: input.query });

// With error object (second arg)
ctx.log.error('Failed to fetch upstream', error, { url, statusCode });

// Debug detail
ctx.log.debug('Cache miss', { key, ttl });

ctx.log vs global logger

Use	Where
ctx.log	Inside tool/resource handlers — auto-correlated to the request
core.logger / logger	In setup(), service constructors, background tasks — no request context available

The global logger is imported from @cyanheads/mcp-ts-core/utils. In handlers, prefer ctx.log.

---

ctx.state

Tenant-scoped key-value storage. Delegates to StorageService with automatic tenantId scoping — data written under tenant A is invisible to tenant B.

Interface

interface ContextState {
  get<T = unknown>(key: string): Promise<T | null>;
  get<T>(key: string, schema: ZodType<T>): Promise<T | null>;  // runtime-validated
  set(key: string, value: unknown, opts?: { ttl?: number }): Promise<void>;
  delete(key: string): Promise<void>;
  deleteMany(keys: string[]): Promise<number>;
  getMany<T = unknown>(keys: string[]): Promise<Map<string, T>>;
  setMany(entries: Map<string, unknown>, opts?: { ttl?: number }): Promise<void>;
  list(prefix?: string, opts?: { cursor?: string; limit?: number }): Promise<{
    items: Array<{ key: string; value: unknown }>;
    cursor?: string;  // opaque base64url; omitted on last page
  }>;
}

Usage

// Store — accepts any serializable value, no manual JSON.stringify needed
await ctx.state.set('item:123', { name: 'Widget', count: 42 });
await ctx.state.set('session:xyz', token, { ttl: 3600 }); // TTL in seconds

// Retrieve — generic type assertion or Zod-validated
const item = await ctx.state.get<Item>('item:123');       // T | null (type assertion)
const safe = await ctx.state.get('item:123', ItemSchema);  // T | null (runtime validated)

// Delete
await ctx.state.delete('item:123');

// Batch operations
const values = await ctx.state.getMany<Item>(['item:1', 'item:2']); // Map<string, T>
await ctx.state.setMany(new Map([['a', 1], ['b', 2]]));
const deleted = await ctx.state.deleteMany(['item:1', 'item:2']);    // number

// List with prefix + pagination
const page = await ctx.state.list('item:', { cursor, limit: 20 });
for (const { key, value } of page.items) { /* ... */ }
if (page.cursor) { /* more pages available */ }

Behavior notes

• Throws McpError(InvalidRequest) if tenantId is missing (won't happen in stdio mode — defaults to 'default').
• Keys are tenant-prefixed internally; handlers never need to namespace manually.
• Workers persistence: The in-memory provider loses data on cold starts. Use cloudflare-kv, cloudflare-r2, or cloudflare-d1 for durable storage in Workers.

---

ctx.elicit / ctx.sample

Both are optional — undefined when the connected client doesn't support the capability. Check for presence before calling. A simple truthiness check is enough; no type guards needed.

ctx.elicit — ask the user for structured input

Presents a form to the user via the MCP elicitation protocol. The user fills in a Zod-validated schema and returns an action (accept, decline, or cancel).

if (ctx.elicit) {
  const result = await ctx.elicit(
    'Which output format do you want?',
    z.object({
      format: z.enum(['json', 'csv', 'markdown']).describe('Output format'),
      includeHeaders: z.boolean().default(true).describe('Include column headers'),
    }),
  );

  if (result.action === 'accept') {
    // result.content is Record<string, string | number | boolean | string[]> | undefined
    await produceOutput(result.content?.format as string, result.content?.includeHeaders as boolean);
  } else {
    // 'decline' or 'cancel' — user opted out
    throw new McpError(JsonRpcErrorCode.InvalidRequest, 'User declined input');
  }
}

ElicitResult (from @modelcontextprotocol/sdk/types.js):

// Actual SDK type — a flat object, not a discriminated union
interface ElicitResult {
  action: 'accept' | 'decline' | 'cancel';
  // Present when action === 'accept'; values are primitives or string arrays
  content?: Record<string, string | number | boolean | string[]>;
}

Note: content is not typed against the Zod schema you pass — it is a Record of primitives. Validate content against your schema manually (e.g. MySchema.parse(result.content)) when action === 'accept'.

Convention: Only call ctx.elicit from tool handlers, not from services.

ctx.sample — request an LLM completion from the client

Requests a completion from the client's LLM via the MCP sampling protocol. Useful for AI-assisted tool behavior without managing a separate LLM provider.

if (ctx.sample) {
  const result = await ctx.sample(
    [
      { role: 'user', content: { type: 'text', text: `Summarize: ${data}` } },
    ],
    { maxTokens: 500 },
  );
  return { summary: result.content.text };
}

SamplingOpts:

interface SamplingOpts {
  includeContext?: 'none' | 'thisServer' | 'allServers';
  maxTokens?: number;
  modelPreferences?: Record<string, unknown>;
  stopSequences?: string[];
  temperature?: number;
}

Convention: Only call ctx.sample from tool handlers, not from services.

---

ctx.signal

Standard AbortSignal. Present on every context. Set when the client cancels the request or when a task tool is cancelled.

// Check before expensive operations
if (ctx.signal.aborted) return earlyResult;

// Pass through to fetch / other async APIs
const response = await fetch(url, { signal: ctx.signal });

// Loop with cancellation check
for (const item of items) {
  if (ctx.signal.aborted) break;
  await processItem(item);
}

In task tools (task: true), the framework signals ctx.signal when the client sends a cancellation request.

---

ctx.progress

Present only when the tool definition includes task: true. Undefined for standard (non-task) tools and all resource handlers.

Methods

Method	Purpose
ctx.progress.setTotal(n)	Set the total number of steps (enables percentage calculation on client)
ctx.progress.increment(amount?)	Advance progress by amount (default: 1)
ctx.progress.update(message)	Send a descriptive status message without advancing the counter

Usage

const asyncCountdown = tool('async_countdown', {
  description: 'Count down from a number with progress updates.',
  task: true,
  input: z.object({
    count: z.number().int().positive().describe('Number to count down from'),
    delayMs: z.number().default(1000).describe('Delay between counts in ms'),
  }),
  output: z.object({
    finalCount: z.number().describe('Final count value'),
    message: z.string().describe('Completion message'),
  }),

  async handler(input, ctx) {
    await ctx.progress!.setTotal(input.count);

    for (let i = input.count; i > 0; i--) {
      if (ctx.signal.aborted) break;

      await ctx.progress!.update(`Counting: ${i}`);
      await new Promise(resolve => setTimeout(resolve, input.delayMs));
      await ctx.progress!.increment();
    }

    return { finalCount: 0, message: 'Countdown complete' };
  },
});

Note: Use the non-null assertion (ctx.progress!) when accessing inside a task: true handler — the type is ContextProgress | undefined even though it's guaranteed present at runtime. TypeScript cannot narrow based on the task flag.

---

ctx.uri

Present only for resource handlers. The raw URL object for the matched resource URI.

export const myResource = resource('myscheme://{itemId}/data', {
  async handler(params, ctx) {
    ctx.log.debug('Resource accessed', { uri: ctx.uri?.toString() });
    // params.itemId is extracted from the URI pattern — prefer params over ctx.uri
    return fetchItem(params.itemId);
  },
});

Prefer params (the extracted URI template variables) over parsing ctx.uri manually. ctx.uri is available when the raw URL string is needed.

---

Quick reference

Property	Type	Present when
ctx.requestId	string	Always
ctx.timestamp	string	Always
ctx.tenantId	string | undefined	Always in stdio ('default'); HTTP with auth
ctx.traceId	string | undefined	OTEL enabled
ctx.spanId	string | undefined	OTEL enabled
ctx.auth	AuthContext | undefined	Auth enabled
ctx.log	ContextLogger	Always
ctx.state	ContextState	Always (throws if tenantId missing)
ctx.signal	AbortSignal	Always
ctx.elicit	function | undefined	Client supports elicitation
ctx.sample	function | undefined	Client supports sampling
ctx.progress	ContextProgress | undefined	Tool defined with task: true
ctx.uri	URL | undefined	Resource handlers only