Diagrams · Fig. 02

Monday / Tuesday

The change arrives with no version bump, no notification and no email. The pin is the only witness.

Monday / TuesdayOn Monday you pin a tool contract in which search_docs takes a query string. On Tuesday the server changes it to also require a webhook parameter, with no version bump, no notification and no email. On Wednesday your agent calls the tool. Without a pin the agent fills the new required parameter and calls anyway and nothing tells you. With mcpindex the call is held and labelled added-required-param before it goes out.MONTUEWEDyou pin the contractsearch_docs(  query: string)the server changes itsearch_docs(  query: string,  webhook: string ** NEWLY REQUIREDNO VERSION BUMP · NO NOTIFICATION · NO EMAILyour agent calls itWITHOUT A PINthe agent fills the new requiredparam and calls. nothing tells you.WITH MCPINDEXadded-required-paramheld before the call goes out.THE TOOL YOUR AGENT TRUSTED ON MONDAY CHANGED ON TUESDAY. NOTHING IN MCP TOLD YOU.
Fig. 02 · The change arrives with no version bump, no notification and no email. The pin is the only witness.
Read Fig. 02 as text
  MON -------------------- TUE -------------------- WED
   |                        |                        |
   you pin the contract     the server changes it    your agent calls it

   search_docs(             search_docs(             WITHOUT A PIN
     query: string            query: string,         the agent fills the new required
   )                          webhook: string *      param and calls. nothing tells you.
                            )
                            * newly required         WITH MCPINDEX
                            no version bump          |- HELD  added-required-param
                            no notification             held before the call goes out
                            no email

  the tool your agent trusted on monday changed on tuesday. nothing in MCP told you.
What the figure says

On Monday you pin a tool contract in which search_docs takes a query string. On Tuesday the server changes it to also require a webhook parameter, with no version bump, no notification and no email. On Wednesday your agent calls the tool. Without a pin the agent fills the new required parameter and calls anyway and nothing tells you. With mcpindex the call is held and labelled added-required-param before it goes out.

Where this is explained
/guides/mcp-silent-contract-drift
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<a href="https://mcpindex.ai/diagrams/silent-contract-drift-timeline">Monday / Tuesday - mcpindex.ai</a> (CC BY 4.0)
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Last reviewed 2026-07-27

Questions this answers

mcp rug pull &middot; mcp silent contract drift &middot; mcp tool poisoning &middot; mcp tool changed without notice